From 140202c5febec6460da00e33d5d14ab69eeaca11 Mon Sep 17 00:00:00 2001
From: Barret Schloerke <barret@posit.co>
Date: Fri, 11 Sep 2026 16:55:04 -0400
Subject: [PATCH 1/3] test: drive servers in memory with test_server() /
 testServer()
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py-shiny#2470 added `shiny.testserver.test_server()`, the Python counterpart
to R's `testServer()`. A ui.tsx server is only reactive computation, so "input
X produces output Y" *is* the server, and both languages can now assert it
with no browser.

Package tests:

- `pkg-py/tests/test_in_memory_server.py` — `reactive_output` publishing
  through a real session (`test_reactive_output.py` only reaches
  `Renderer.transform()`), module namespace isolation via `make_scope()`, and
  output error statuses. Reuses the Playwright fixture apps; needs no e2e
  extras, so it lives in the unit suite.
- `pkg-r/tests/testthat/test-render.R` — the R mirrors of those two, with the
  divergence stated: R's `testServer()` re-raises where Python reports
  `.status`.

Example tests, one per app with a Python server, plus R counterparts for the
two that ship an `app.R` (07-plotly had no R test directory):

- two `FEATURES.md` leaves were wrong and are now correct and tested:
  05-temperature and 08-input-handler both claimed `input.x()` is `None`
  before the client's first message, so the server returns `None` / `"—"`. It
  raises a silent exception, so those branches are unreachable from a real
  client.
- `(test)` markers added across seven example trees for the wire shapes,
  thresholds, pluralization, event handling, and `AsIs` wrapping these pin.

Docs and skills:

- the Quarto article and its R vignette mirror are retitled "Testing" and gain
  a server-testing half ahead of the wire-tap material.
- `shinyreact-build-app/references/testing.md` said "`[py]` has no
  `testServer()` equivalent … This is a real gap"; it now documents
  `test_server()`, and `shinyreact-convert-app`'s verify phase goes from three
  layers to four. Shipped copies refreshed with `make update-skills`.
- documented, because each cost time to find: pass an absolute `Path`; an
  untyped id needs no `:shinyreact.default` suffix but a typed id does; an
  event input needs two `set_inputs` calls; an unset input is `status ==
  "silent"`, not a `None` value.

`test_server()` is newer than shiny 1.7.0, which the docs and skills say
explicitly.

Two upstream issues filed from this work: posit-dev/py-shiny#2492 (a silent
`req()` failure is invisible in memory — `get_output()` keeps the stale value
while the browser blanks the output) and posit-dev/py-shiny#2493 (`status ==
"silent"` means "never rendered", inverting Shiny's own meaning).

Drive-by: `test-examples.R` read every file in an example directory before
filtering to `app.R` + `www/`, so `__pycache__` produced 208 `readLines()`
warnings.
---
 .claude/skills/shinyreact-build-app/SKILL.md  | 23 +++--
 .../references/testing.md                     | 86 ++++++++++++++---
 .../skills/shinyreact-convert-app/SKILL.md    | 16 ++--
 examples/01-hello/FEATURES.md                 | 15 ++-
 examples/01-hello/tests/test_outputs.py       | 62 +++++++++++++
 .../01-hello/tests/testthat/test-outputs.R    | 66 +++++++++++++
 examples/02-columns/FEATURES.md               | 14 ++-
 examples/02-columns/tests/test_moves.py       | 64 +++++++++++++
 examples/05-temperature/FEATURES.md           | 16 ++--
 examples/05-temperature/tests/test_display.py | 66 +++++++++++++
 examples/06-data-frame/FEATURES.md            | 12 ++-
 examples/06-data-frame/tests/test_table.py    | 42 +++++++++
 examples/07-plotly/FEATURES.md                | 14 ++-
 examples/07-plotly/tests/test_scatter.py      | 43 +++++++++
 examples/07-plotly/tests/testthat.R           | 10 ++
 .../07-plotly/tests/testthat/test-outputs.R   | 54 +++++++++++
 examples/08-input-handler/FEATURES.md         | 11 ++-
 examples/08-input-handler/tests/test_when.py  | 46 ++++++++++
 examples/10-bookmarking/FEATURES.md           | 10 +-
 .../10-bookmarking/tests/test_greeting.py     | 51 ++++++++++
 examples/README.md                            | 20 ++++
 pkg-py/README.md                              |  2 +-
 pkg-py/docs/_quarto.yml                       |  3 +-
 pkg-py/docs/articles/testing.qmd              | 84 +++++++++++++++--
 .../skills/shinyreact-build-app/SKILL.md      | 23 +++--
 .../references/testing.md                     | 86 ++++++++++++++---
 .../skills/shinyreact-convert-app/SKILL.md    | 16 ++--
 pkg-py/tests/test_in_memory_server.py         | 92 +++++++++++++++++++
 pkg-r/README.md                               |  2 +-
 .../inst/skills/shinyreact-build-app/SKILL.md | 23 +++--
 .../references/testing.md                     | 86 ++++++++++++++---
 .../skills/shinyreact-convert-app/SKILL.md    | 16 ++--
 pkg-r/tests/testthat/test-examples.R          | 15 ++-
 pkg-r/tests/testthat/test-render.R            | 67 ++++++++++++++
 pkg-r/vignettes/articles/testing.Rmd          | 74 +++++++++++++--
 pkg-r/vignettes/shinyreact.Rmd                |  5 +-
 36 files changed, 1200 insertions(+), 135 deletions(-)
 create mode 100644 examples/01-hello/tests/test_outputs.py
 create mode 100644 examples/01-hello/tests/testthat/test-outputs.R
 create mode 100644 examples/02-columns/tests/test_moves.py
 create mode 100644 examples/05-temperature/tests/test_display.py
 create mode 100644 examples/06-data-frame/tests/test_table.py
 create mode 100644 examples/07-plotly/tests/test_scatter.py
 create mode 100644 examples/07-plotly/tests/testthat.R
 create mode 100644 examples/07-plotly/tests/testthat/test-outputs.R
 create mode 100644 examples/08-input-handler/tests/test_when.py
 create mode 100644 examples/10-bookmarking/tests/test_greeting.py
 create mode 100644 pkg-py/tests/test_in_memory_server.py

diff --git a/.claude/skills/shinyreact-build-app/SKILL.md b/.claude/skills/shinyreact-build-app/SKILL.md
index 0a922ace..0a225bee 100644
--- a/.claude/skills/shinyreact-build-app/SKILL.md
+++ b/.claude/skills/shinyreact-build-app/SKILL.md
@@ -383,8 +383,8 @@ a list. Use `type: "shinyreact.asis"` for the parsed value untouched.
 Do not stop at "the code is written". Three steps, in order:
 
 1. **Factor pure logic out of the app file** — binning, formatting,
-   conversions go in a module beside the app. Logic inside `app.py` /
-   `app.R` next to the page call cannot be reached by a test at all.
+   conversions go in a module beside the app, where a test can import them
+   without starting a session at all.
 2. **Write down what the app does, in plain English, before the tests.** An
    agent that writes the client and then writes the client's tests is
    agreeing with itself — both encode the same misunderstanding. A
@@ -394,16 +394,19 @@ Do not stop at "the code is written". Three steps, in order:
    directory** — `pytest`, or `[r]` `shiny::runTests()`, which needs the
    `tests/testthat.R` + `tests/testthat/` layout.
 
-`[r]` `shiny::testServer()` drives the reactive graph with no browser:
-`session$setInputs(bins = 9)` then assert on `output$dist_data`, which is the
-JSON value the client would have received. **`[py]` has no equivalent**, so
-factoring logic into an importable module matters more there.
+Both languages drive the reactive graph with no browser, which for a `ui.tsx`
+app is most of the server: `[r]` `shiny::testServer()` (`session$setInputs(bins
+= 9)`, then assert on `output$dist_data`) and `[py]`
+`shiny.testserver.test_server()` (`ts.set_inputs(bins=9)`, then
+`ts.get_output("dist_data")`). Either way the value you assert is the JSON the
+client would have received.
 
 [`references/testing.md`](references/testing.md) has the four layers, the test
-layout for each language, `testServer()` for plain and module servers, how to
-mount the real `www/ui.js` against a fake Shiny, and the traps that cost time
-(React ignores raw `change` events; debounce coalesces within a tick even at
-`debounceMs: 0`).
+layout for each language, `testServer()` / `test_server()` for plain and module
+servers — including the input ids that need a `:type` suffix and the event
+inputs that need two `set_inputs` calls — how to mount the real `www/ui.js`
+against a fake Shiny, and the traps that cost time (React ignores raw `change`
+events; debounce coalesces within a tick even at `debounceMs: 0`).
 
 ## Debugging
 
diff --git a/.claude/skills/shinyreact-build-app/references/testing.md b/.claude/skills/shinyreact-build-app/references/testing.md
index 8fa6e978..245ede5e 100644
--- a/.claude/skills/shinyreact-build-app/references/testing.md
+++ b/.claude/skills/shinyreact-build-app/references/testing.md
@@ -3,8 +3,11 @@
 Do not stop at "the code is written". At minimum:
 
 1. **Factor pure logic out of the app file.** Binning, formatting, conversions
-   go in a module beside the app so a test can import them; logic sitting
-   inside `app.py` / `app.R` next to the page call cannot be reached at all.
+   go in a module beside the app so a test can import them directly, with no
+   session at all. Logic left inside `app.py` / `app.R` next to the page call
+   is still reachable — `testServer()` / `test_server()` below drive the app
+   itself — but only through an input, which is a slower and blunter tool than
+   calling a function.
 2. **Write down what the app does, in plain English, before the tests** — a
    behavior file beside the app, one atomically checkable claim per line
    ("the caption reads `N eruptions in M bins`, singular `bin` at M=1"). An
@@ -16,7 +19,7 @@ Do not stop at "the code is written". At minimum:
 | Layer | Proves | Cost |
 |---|---|---|
 | pure functions in their own module | binning, formatting, conversions | trivial — always do this |
-| `[r]` `shiny::testServer()` | the reactive graph: inputs in, `reactive_output` values out | low, and no browser |
+| `shiny::testServer()` `[r]` / `shiny.testserver.test_server()` `[py]` | the reactive graph: inputs in, `reactive_output` values out | low, and no browser |
 | the client mounted in jsdom against a fake Shiny | rendering, input wiring, wire ids, status handling | low, and it exercises the file the app ships |
 | Playwright | layout, real Shiny, real bindings | high; reserve for what the others cannot see |
 
@@ -31,7 +34,8 @@ myapp/
   faithful.py            the factored logic
   www/ui.js
   tests/
-    test_faithful.py     [py]  pytest
+    test_faithful.py     [py]  pytest — the factored logic, called directly
+    test_outputs.py      [py]  pytest — the app, via test_server()
     testthat.R           [r]   runner: library(testthat); test_dir("testthat")
     testthat/
       test-histogram.R   [r]
@@ -58,11 +62,17 @@ sys.path.insert(0, str(EXAMPLE))
 from faithful import histogram, waiting  # noqa: E402
 ```
 
-## `[r]` Testing the server with `testServer()`
+## Testing the server: `testServer()` `[r]`, `test_server()` `[py]`
 
-`reactive_output` is an ordinary Shiny render function, so `shiny::testServer()`
-drives it with no browser and no client: set inputs, read outputs, and get the
-JSON value the client would have received.
+**This is the highest-value layer for a `ui.tsx` app.** The server contains
+only reactive computation, so "input X produces output Y" *is* the server, and
+both languages can assert it with no browser and no client: set inputs, read
+outputs, and get the JSON value the client would have received.
+
+### `[r]` `shiny::testServer()`
+
+`reactive_output` is an ordinary Shiny render function, so `testServer()`
+drives it directly.
 
 ```r
 test_that("the histogram recomputes when bins changes", {
@@ -90,10 +100,62 @@ which is most of what a shinyreact server does.
 Module servers work the same way: `testServer(card_server, args = list(id =
 "left"), { ... })`.
 
-**`[py]` has no `testServer()` equivalent.** Cover the Python server by
-factoring its logic into a module and testing that with pytest, and let the
-jsdom and Playwright layers cover the wiring. This is a real gap, not an
-oversight in your app.
+### `[py]` `shiny.testserver.test_server()`
+
+The Python counterpart (py-shiny#2470, so newer than shiny 1.7.0). It loads the
+app file — Express or Core, `shiny.App` or `shinyreact.ReactApp` — and runs its
+server against a mock connection:
+
+```python
+from pathlib import Path
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_the_histogram_recomputes_when_bins_changes():
+    with test_server(APP) as ts:
+        ts.set_inputs(bins=9)
+        assert ts.get_output("dist_data").value["counts"] == [16, 37, 30, 16, 14, 57, 67, 29, 6]
+        assert ts.get_output("dist_caption") == "272 eruptions in 9 bins"
+```
+
+`get_output()` returns a value that compares equal to the underlying one, so
+assert on it directly; use `.value` when you need to index into it, and
+`.status` (`"ok"` / `"error"` / `"silent"`) or `.error` to assert the
+non-value outcomes. Traditional renderers are readable too, so
+`@render.data_frame` / `@render_plotly` outputs mounted through `ShinyOutput`
+can be checked at the wire level.
+
+Pass an **absolute `Path`**: a relative one resolves against the test file's
+directory, and the app is a directory up from `tests/`.
+
+Four things to know, all of them shinyreact-specific:
+
+- **An untyped input id needs no `:shinyreact.default` suffix.** The hook
+  appends it on the wire, but both Python handlers are no-ops, so
+  `set_inputs(bins=9)` is equivalent.
+- **A typed one does.** `set_inputs(**{"when:shiny.datetime": 1756382400})` is
+  what makes the handler run and `input.when()` a `datetime`; without the
+  suffix you are testing a different app than the one the client drives.
+- **An event input needs two calls.** `useShinyInput` registers its default at
+  mount and sends the event after, so an output behind
+  `@reactive.event(..., ignore_init=True)` only fires on the *second*
+  `set_inputs` for that id.
+- **An unset input means `status == "silent"`, not a `None` value.**
+  `input.x()` raises a silent exception while unset, so a `if x is None:`
+  branch in your server is unreachable from a real client — assert the status
+  instead. (A *later* `req()` failure is not visible in memory at all:
+  py-shiny#2492.)
+
+Module ids can be read as the session sees them (`ts.get_output("counter-n")`)
+or through a scope, which strips the namespace on the way in and out:
+
+```python
+with ts.make_scope("counter") as counter:
+    counter.set_inputs(n=7)
+    assert counter.get_output("label") == "n=7"
+```
 
 ## The jsdom layer — mount the client the app ships
 
diff --git a/.claude/skills/shinyreact-convert-app/SKILL.md b/.claude/skills/shinyreact-convert-app/SKILL.md
index ed308117..c8184922 100644
--- a/.claude/skills/shinyreact-convert-app/SKILL.md
+++ b/.claude/skills/shinyreact-convert-app/SKILL.md
@@ -149,12 +149,16 @@ rendered), then the rest of the outputs, then layout and polish.
 
 ## Phase 5 — verify
 
-Three layers, cheapest first: factor pure logic out of the app file so it is
-importable and test it directly; test the client by evaluating the real
-`www/ui.js` against a fake `window.Shiny` in jsdom (not by importing the
-component — that tests a copy the app does not ship); and reserve Playwright
-for layout and real bindings, which the other two structurally cannot see. The
-`shinyreact-build-app` skill's `references/testing.md` has the traps.
+Four layers, cheapest first: factor pure logic out of the app file so it is
+importable and test it directly; drive the ported server with no browser —
+`[r]` `shiny::testServer()`, `[py]` `shiny.testserver.test_server()` — which
+for a `ui.tsx` app covers most of it, since the server is only reactive
+computation; test the client by evaluating the real `www/ui.js` against a fake
+`window.Shiny` in jsdom (not by importing the component — that tests a copy the
+app does not ship); and reserve Playwright for layout and real bindings, which
+the others structurally cannot see. The `shinyreact-build-app` skill's
+[`references/testing.md`](../shinyreact-build-app/references/testing.md) has
+the details and the traps.
 
 A port has one advantage a new app does not: **the original still runs.** Where
 the logic is a pure transform, capture its output from the original app and
diff --git a/examples/01-hello/FEATURES.md b/examples/01-hello/FEATURES.md
index a634ab18..14cd7ef8 100644
--- a/examples/01-hello/FEATURES.md
+++ b/examples/01-hello/FEATURES.md
@@ -20,7 +20,8 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
 
 ## Server
 
-- output `dist_data` → `{breaks: number[], counts: number[]}`
+- output `dist_data` → `{breaks: number[], counts: number[]}` `(test)`
+  - the two keys, in that order, and nothing else `(test)`
   - equal-width bins over `[min, max]`: `breaks` has `bins + 1` entries,
     `counts` has `bins` `(test)`
   - binning matches R's `hist()`: half-open `(lo, hi]` with the first bin
@@ -35,16 +36,20 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
   - `bins = 9` → `counts == [16, 37, 30, 16, 14, 57, 67, 29, 6]`, identical in
     R and Python `(test)`
   - `[r]` vectors are wrapped in `I()` so a one-bin result serializes as a JSON
-    array, not a scalar
-- output `dist_caption` → `"272 eruptions in N bins"`
+    array, not a scalar — the value the output delivers carries the `AsIs`
+    class `(test)`
+- output `dist_caption` → `"272 eruptions in N bins"` `(test)`
   - singular `"bin"` when `N == 1` `(test)`
   - the count is the dataset length, not the bin count
+- `[py]` `app.py` (Express) and `app-core.py` (Core) produce identical values
+  for both outputs — the same `tests/test_outputs.py` runs against each
+  `(test)`
 - before the client's first `bins` message
   - `[py]` `input.bins()` raises a silent exception, so neither output produces
-    a value
+    a value — not an error, and not a `None` value `(test)`
   - `[r]` `input$bins` is `NULL` and both outputs return `NULL` explicitly —
     `req()` is deliberately not used, because its silent error still reaches
-    the client console
+    the client console `(test)`
 - the server never renders an image: no plotting library, no `plotOutput`
   placeholder
 
diff --git a/examples/01-hello/tests/test_outputs.py b/examples/01-hello/tests/test_outputs.py
new file mode 100644
index 00000000..1d1db9b3
--- /dev/null
+++ b/examples/01-hello/tests/test_outputs.py
@@ -0,0 +1,62 @@
+"""Pins this example's server outputs as the client sees them.
+
+`test_faithful.py` next to this file tests the binner as a pure function;
+this file drives the *app* — `shiny.testserver.test_server()` runs the server
+against a mock connection, so `dist_data` and `dist_caption` can be asserted
+exactly as they arrive at `useShinyOutputValue()`. No browser, no subprocess.
+
+Both Python servers are covered, because `app.py` (Express) and `app-core.py`
+(Core) are claimed to be interchangeable over one `www/` client.
+
+Run it from the app directory, the way a user of the app would::
+
+    pytest
+
+An input id needs no `:shinyreact.default` suffix here: the React hook appends
+it on the wire, but Python's handler is a no-op, so `set_inputs(bins=9)`
+reaches the server identically.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from shiny.testserver import test_server
+
+EXAMPLE = Path(__file__).resolve().parents[1]
+APPS = [EXAMPLE / "app.py", EXAMPLE / "app-core.py"]
+
+# Mirrored in test_faithful.py, tests/test-histogram.R and tests/ui.test.ts.
+COUNTS_9 = [16, 37, 30, 16, 14, 57, 67, 29, 6]
+
+
+@pytest.mark.parametrize("app", APPS, ids=lambda p: p.name)
+def test_dist_data_wire_shape(app: Path) -> None:
+    with test_server(app) as ts:
+        ts.set_inputs(bins=9)
+        data = ts.get_output("dist_data").value
+        assert list(data) == ["breaks", "counts"]
+        assert data["counts"] == COUNTS_9
+        assert data["breaks"][0] == 43.0
+        assert data["breaks"][-1] == pytest.approx(96.0)
+
+
+@pytest.mark.parametrize("app", APPS, ids=lambda p: p.name)
+def test_dist_caption_pluralizes(app: Path) -> None:
+    with test_server(app) as ts:
+        ts.set_inputs(bins=9)
+        assert ts.get_output("dist_caption") == "272 eruptions in 9 bins"
+
+        ts.set_inputs(bins=1)
+        assert ts.get_output("dist_caption") == "272 eruptions in 1 bin"
+        assert ts.get_output("dist_data").value["counts"] == [272]
+
+
+@pytest.mark.parametrize("app", APPS, ids=lambda p: p.name)
+def test_neither_output_renders_before_the_first_bins_message(app: Path) -> None:
+    # `input.bins()` raises a silent exception while unset, so both outputs
+    # have no value at all — not an error, and not a `None` value.
+    with test_server(app) as ts:
+        assert ts.get_output("dist_data").status == "silent"
+        assert ts.get_output("dist_caption").status == "silent"
diff --git a/examples/01-hello/tests/testthat/test-outputs.R b/examples/01-hello/tests/testthat/test-outputs.R
new file mode 100644
index 00000000..817ea0b6
--- /dev/null
+++ b/examples/01-hello/tests/testthat/test-outputs.R
@@ -0,0 +1,66 @@
+# Pins app.R's outputs as the client sees them, using shiny::testServer() --
+# inputs in, output values out, with no browser and no client.
+#
+# test-histogram.R next door pins the *math* by reimplementing app.R's two
+# lines, because that logic lives inside server(). This file drives server()
+# itself, so it pins what the app actually answers with. The Python
+# counterpart is test_outputs.py beside them, which does the same thing with
+# shiny.testserver.test_server().
+#
+# Run it from the app directory, the way a user of the app would:
+#
+#   Rscript -e 'shiny::runTests()'
+#   Rscript -e 'testthat::test_dir("tests/testthat")'
+#
+# The shinyreact package's own suite also runs it, via
+# pkg-r/tests/testthat/test-examples.R.
+#
+# app_dir is "../../" from tests/testthat/, the same default AppDriver uses.
+app_dir <- testthat::test_path("..", "..")
+
+test_that("dist_data is the {breaks, counts} the client draws", {
+  shiny::testServer(app_dir, {
+    session$setInputs(bins = 9)
+
+    expect_named(output$dist_data, c("breaks", "counts"))
+    # Mirrors COUNTS_9 in test_faithful.py and test-histogram.R.
+    expect_equal(
+      unclass(output$dist_data$counts),
+      c(16L, 37L, 30L, 16L, 14L, 57L, 67L, 29L, 6L)
+    )
+    expect_equal(unclass(output$dist_data$breaks)[[1]], 43)
+    expect_equal(unclass(output$dist_data$breaks)[[10]], 96)
+  })
+})
+
+test_that("dist_caption pluralizes on the bin count", {
+  shiny::testServer(app_dir, {
+    session$setInputs(bins = 9)
+    expect_equal(output$dist_caption, "272 eruptions in 9 bins")
+
+    session$setInputs(bins = 1)
+    expect_equal(output$dist_caption, "272 eruptions in 1 bin")
+    expect_equal(unclass(output$dist_data$counts), 272L)
+    expect_equal(unclass(output$dist_data$breaks), c(43, 96))
+  })
+})
+
+test_that("the vectors carry I(), so a one-bin result is a JSON array", {
+  # The class is the behavior: without it toJSON() emits `272` where the
+  # client expects `[272]`. test-histogram.R pins the serialization; this
+  # pins that app.R really applies it.
+  shiny::testServer(app_dir, {
+    session$setInputs(bins = 1)
+    expect_s3_class(output$dist_data$counts, "AsIs")
+    expect_s3_class(output$dist_data$breaks, "AsIs")
+  })
+})
+
+test_that("both outputs are NULL before the client's first bins message", {
+  # app.R returns NULL explicitly rather than using req(), so there is no
+  # silent error to reach the client console.
+  shiny::testServer(app_dir, {
+    expect_null(output$dist_data)
+    expect_null(output$dist_caption)
+  })
+})
diff --git a/examples/02-columns/FEATURES.md b/examples/02-columns/FEATURES.md
index 30afd28b..45ab0a61 100644
--- a/examples/02-columns/FEATURES.md
+++ b/examples/02-columns/FEATURES.md
@@ -17,18 +17,22 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
 
 ## Server (`app.py`, Express)
 
-- output `column_data` → the whole `{col: item[]}` dict
+- output `column_data` → the whole `{col: item[]}` dict `(test)`
+  - it renders from the initial contents before any input arrives `(test)`
 - input `move_item` → `{item, from, to}`
   - handled by a `@reactive.effect` + `@reactive.event(input.move_item,
-    ignore_init=True)`, so the initial `null` from mount is ignored
+    ignore_init=True)`, so the initial `null` from mount is ignored `(test)`
   - the move is applied to a copy of the dict, then `columns.set(...)` — the
     reactive value is replaced, not mutated in place
-  - if `item` is not in `data[from]`, nothing changes (no error)
+  - if `item` is not in `data[from]`, nothing changes (no error) `(test)`
   - the item is appended to the end of the destination column, never inserted
+    `(test)`
+  - successive moves accumulate `(test)`
 - `[py]` only — this example has no R server
 - the server logic lives inside `app.py` next to `set_react_page()`, so it is
-  not importable and no unit test covers it — logic in a module beside `app.py`
-  would be testable
+  not importable — `tests/test_moves.py` drives the app itself with
+  `shiny.testserver.test_server()` instead, sending the mount-time `null`
+  first so the move is not swallowed as the init
 
 ## Client (`www/ui.js`)
 
diff --git a/examples/02-columns/tests/test_moves.py b/examples/02-columns/tests/test_moves.py
new file mode 100644
index 00000000..9b8b79b3
--- /dev/null
+++ b/examples/02-columns/tests/test_moves.py
@@ -0,0 +1,64 @@
+"""Pins the server's move handling as the client drives it.
+
+`shiny.testserver.test_server()` runs `app.py`'s server against a mock
+connection, so the `move_item` → `column_data` round trip can be asserted
+without a browser. Run it from the app directory::
+
+    pytest
+
+`move_item` is an **event** input (`@reactive.event(..., ignore_init=True)`),
+so a test has to mirror what the client does: `useShinyInput("move_item",
+null)` registers the `null` default at mount, and the drop sends the move
+after. With a single `set_inputs` the move *is* the init and is ignored.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+INITIAL = {
+    "A": ["Apple", "Apricot"],
+    "B": ["Banana", "Blueberry"],
+    "C": ["Cherry", "Cranberry"],
+}
+
+
+def test_column_data_starts_at_the_initial_three_columns() -> None:
+    with test_server(APP) as ts:
+        assert ts.get_output("column_data") == INITIAL
+
+
+def test_a_move_removes_from_the_source_and_appends_to_the_target() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(move_item=None)  # the hook's default, sent at mount
+        ts.set_inputs(move_item={"item": "Apple", "from": "A", "to": "C"})
+
+        assert ts.get_output("column_data") == {
+            "A": ["Apricot"],
+            "B": ["Banana", "Blueberry"],
+            # Appended, not inserted in sorted position.
+            "C": ["Cherry", "Cranberry", "Apple"],
+        }
+
+
+def test_a_move_of_an_item_the_source_does_not_hold_is_ignored() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(move_item=None)
+        ts.set_inputs(move_item={"item": "Cherry", "from": "A", "to": "B"})
+        assert ts.get_output("column_data") == INITIAL
+
+
+def test_moves_accumulate() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(move_item=None)
+        ts.set_inputs(move_item={"item": "Apple", "from": "A", "to": "B"})
+        ts.set_inputs(move_item={"item": "Apple", "from": "B", "to": "C"})
+
+        data = ts.get_output("column_data").value
+        assert data["A"] == ["Apricot"]
+        assert data["B"] == ["Banana", "Blueberry"]
+        assert data["C"] == ["Cherry", "Cranberry", "Apple"]
diff --git a/examples/05-temperature/FEATURES.md b/examples/05-temperature/FEATURES.md
index f73b1972..6203b3bc 100644
--- a/examples/05-temperature/FEATURES.md
+++ b/examples/05-temperature/FEATURES.md
@@ -9,19 +9,23 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
 
 ## Server (`app.py`, Express)
 
-- one output, `display` → `{celsius, fahrenheit, zone}`
+- one output, `display` → `{celsius, fahrenheit, zone}` `(test)`
 - `fahrenheit` is `round(c * 9 / 5 + 32, 1)` — one decimal, so 20 °C → 68.0
-- `zone` thresholds, all inclusive upper bounds
+  `(test)`
+  - the client rounds to whole degrees, so the two disagree by design: 37 °C is
+    `98.6` from the server and `99` on the client `(test)`
+- `zone` thresholds, all inclusive upper bounds `(test)`
   - `c <= 0` → `"Freezing"`
   - `c <= 15` → `"Cold"`
   - `c <= 30` → `"Comfortable"`
   - otherwise → `"Hot"`
-- `input.celsius()` is `None` before the client's first message → returns
-  `None`, so the echo line does not render
+- before the client's first message, `input.celsius()` raises a silent
+  exception, so `display` never renders — the `c is None` guard in `app.py` is
+  unreachable from a real client `(test)`
 - `[py]` only — this example has no R server
 - the logic lives inside `app.py` next to `set_react_page()`, so it is not
-  importable and no unit test covers it — logic in a module beside `app.py`
-  would be testable
+  importable — `tests/test_display.py` drives the app itself with
+  `shiny.testserver.test_server()` instead
 
 ## Client (`www/ui.js`)
 
diff --git a/examples/05-temperature/tests/test_display.py b/examples/05-temperature/tests/test_display.py
new file mode 100644
index 00000000..b49b2ae9
--- /dev/null
+++ b/examples/05-temperature/tests/test_display.py
@@ -0,0 +1,66 @@
+"""Pins the server echo — the half of this example the client does not compute.
+
+The client converts locally and the server converts again; a threshold or
+rounding change on one side without the other is a visible divergence, so both
+sides need a test. `ui.test.ts` next to this file covers the client;
+`shiny.testserver.test_server()` covers the server, in memory. Run it from the
+app directory::
+
+    pytest
+
+The client rounds to whole degrees while the server keeps one decimal — the
+`98.6` below is the server's answer for the same 37 °C the client shows as
+`99°F`, which is exactly the divergence worth pinning.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_display_wire_shape() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(celsius=20)
+        assert ts.get_output("display") == {
+            "celsius": 20,
+            "fahrenheit": 68.0,
+            "zone": "Comfortable",
+        }
+
+
+def test_fahrenheit_keeps_one_decimal() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(celsius=37)
+        assert ts.get_output("display").value["fahrenheit"] == 98.6
+
+
+@pytest.mark.parametrize(
+    "celsius, zone",
+    [
+        (-40, "Freezing"),
+        (0, "Freezing"),  # inclusive upper bound
+        (1, "Cold"),
+        (15, "Cold"),
+        (16, "Comfortable"),
+        (30, "Comfortable"),
+        (31, "Hot"),
+        (60, "Hot"),
+    ],
+)
+def test_zone_thresholds(celsius: int, zone: str) -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(celsius=celsius)
+        assert ts.get_output("display").value["zone"] == zone
+
+
+def test_no_echo_before_the_clients_first_message() -> None:
+    # `input.celsius()` raises a silent exception while unset, so `display`
+    # never renders at all — the `c is None` guard in `app.py` is unreachable
+    # from a real client.
+    with test_server(APP) as ts:
+        assert ts.get_output("display").status == "silent"
diff --git a/examples/06-data-frame/FEATURES.md b/examples/06-data-frame/FEATURES.md
index e3bd1a59..0069cfab 100644
--- a/examples/06-data-frame/FEATURES.md
+++ b/examples/06-data-frame/FEATURES.md
@@ -9,13 +9,17 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
 
 ## Server (`app.py`, Express)
 
-- output `greeting` (`reactive_output`) → `"Showing N rows"`
+- output `greeting` (`reactive_output`) → `"Showing N rows"` `(test)`
   - no singular special case: `N = 1` reads `"Showing 1 rows"`
 - output `my_table` (`@render.data_frame`) → a pandas DataFrame with `N` rows
-  and columns `Name` / `Value` / `Category`
-  - `Name` is `"Item 1" … "Item N"`, 1-based
-  - `Value` is `10, 20, … 10N`
+  and columns `Name` / `Value` / `Category` `(test)`
+  - `Name` is `"Item 1" … "Item N"`, 1-based `(test)`
+  - `Value` is `10, 20, … 10N` `(test)`
   - `Category` is `"A"` on even `i`, `"B"` on odd `i` — so row 1 is `B`
+    `(test)`
+  - on the wire it is `{payload: {columns, data, typeHints, …}}` — row-major
+    `data`, one array per row `(test)`
+- `row_count` drives both outputs `(test)`
 - there is no `ui.output_data_frame("my_table")` anywhere; the element the
   binding attaches to is created by the client
 - `set_react_page()` discovers the data-frame renderer's `HTMLDependency` and
diff --git a/examples/06-data-frame/tests/test_table.py b/examples/06-data-frame/tests/test_table.py
new file mode 100644
index 00000000..ad0f4937
--- /dev/null
+++ b/examples/06-data-frame/tests/test_table.py
@@ -0,0 +1,42 @@
+"""Pins both outputs, including the traditional `@render.data_frame` one.
+
+`shiny.testserver.test_server()` reads a `reactive_output` and a traditional
+renderer the same way, so the payload `ShinyOutput` hands to
+`shiny-data-frame` can be asserted in memory. Run it from the app directory::
+
+    pytest
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_greeting_counts_the_rows() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(row_count=3)
+        assert ts.get_output("greeting") == "Showing 3 rows"
+
+
+def test_data_frame_payload() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(row_count=3)
+        payload = ts.get_output("my_table").value["payload"]
+
+        assert payload["columns"] == ["Name", "Value", "Category"]
+        assert payload["data"] == [
+            ["Item 1", 10, "B"],
+            ["Item 2", 20, "A"],
+            ["Item 3", 30, "B"],
+        ]
+
+
+def test_row_count_drives_both_outputs() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(row_count=5)
+        assert ts.get_output("greeting") == "Showing 5 rows"
+        assert len(ts.get_output("my_table").value["payload"]["data"]) == 5
diff --git a/examples/07-plotly/FEATURES.md b/examples/07-plotly/FEATURES.md
index ffcdbd59..efb895a2 100644
--- a/examples/07-plotly/FEATURES.md
+++ b/examples/07-plotly/FEATURES.md
@@ -10,21 +10,31 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
 
 ## Server
 
-- output `greeting` (`reactive_output`) → `"Showing N random points"`
+- output `greeting` (`reactive_output`) → `"Showing N random points"` `(test)`
+  - no singular special case: `N = 1` reads `"Showing 1 random points"`
+    `(test)`
   - `[r]` returns `NULL` while `input$num_points` is `NULL`; `req()` is
     deliberately avoided so the silent error does not reach the client console
+    `(test)`
   - `[py]` `input.num_points()` raises a silent exception before the first
-    message
+    message, so neither output renders `(test)`
 - output `scatter` — a Plotly figure of `N` standard-normal `(x, y)` points,
   seeded 42, title `"Random Scatter (N points)"`, margins l 40 / r 20 / t 40 /
   b 40
   - `[py]` `@render_plotly` from shinywidgets, `px.scatter` over
     `np.random.default_rng(42)`
   - `[r]` `plotly::renderPlotly` with `set.seed(42)` and `rnorm`
+    - on the wire it is a `json` string carrying the figure, with the widget's
+      own dependencies (`plotly-main`, `crosstalk`, …) attached to it — but
+      **not** `plotly-binding`, which arrives separately `(test)`
   - the two servers draw *different* points — the RNG streams differ — so this
     is not a cross-language parity claim
   - `[r]` uses `req(input$num_points)` here, unlike `greeting`
+  - `[py]` on the wire it is a widget reference, not a figure:
+    `{model_id, fill, widget_pkg: "plotly"}` — the client's `ShinyOutput` is
+    what turns it into a plot `(test)`
 - there is no `output_widget()` / `plotlyOutput()` placeholder in either server
+  — the value is produced all the same `(test)`
 - the render function's binding JS is discovered and delivered automatically
   - `[py]` `set_react_page()` inlines the dependency into `<head>`
   - `[r]` `page_react()` cannot inline it (the UI is built before `server()`
diff --git a/examples/07-plotly/tests/test_scatter.py b/examples/07-plotly/tests/test_scatter.py
new file mode 100644
index 00000000..ffd9340d
--- /dev/null
+++ b/examples/07-plotly/tests/test_scatter.py
@@ -0,0 +1,43 @@
+"""Pins both outputs: the JSON echo and the plotly widget.
+
+`shiny.testserver.test_server()` reads a `reactive_output` and a
+`@render_plotly` widget the same way, so this example's central claim — a
+traditional widget renderer needs no `*Output()` placeholder to produce its
+value — is checkable without a browser. Run it from the app directory::
+
+    pytest
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_greeting_counts_the_points() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(num_points=50)
+        assert ts.get_output("greeting") == "Showing 50 random points"
+
+        ts.set_inputs(num_points=1)
+        assert ts.get_output("greeting") == "Showing 1 random points"
+
+
+def test_scatter_renders_a_widget_with_no_placeholder() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(num_points=50)
+        widget = ts.get_output("scatter").value
+
+        # What shinywidgets puts on the wire: a widget reference, not a figure.
+        # The client's `ShinyOutput` is what turns it into a plot.
+        assert widget["widget_pkg"] == "plotly"
+        assert widget["model_id"]
+
+
+def test_neither_output_renders_before_the_first_message() -> None:
+    with test_server(APP) as ts:
+        assert ts.get_output("greeting").status == "silent"
+        assert ts.get_output("scatter").status == "silent"
diff --git a/examples/07-plotly/tests/testthat.R b/examples/07-plotly/tests/testthat.R
new file mode 100644
index 00000000..ee81e5d0
--- /dev/null
+++ b/examples/07-plotly/tests/testthat.R
@@ -0,0 +1,10 @@
+# Runner for this example app's own tests, in the layout `shiny::runTests()`
+# and `shinytest2::test_app()` expect. From the app directory:
+#
+#   Rscript -e 'shiny::runTests()'
+#
+# The Python and JS tests for this app live beside testthat/ and are run with
+# pytest and vitest; see examples/README.md.
+library(testthat)
+
+test_dir("testthat")
diff --git a/examples/07-plotly/tests/testthat/test-outputs.R b/examples/07-plotly/tests/testthat/test-outputs.R
new file mode 100644
index 00000000..a1f198d2
--- /dev/null
+++ b/examples/07-plotly/tests/testthat/test-outputs.R
@@ -0,0 +1,54 @@
+# Pins app.R's outputs with shiny::testServer() -- no browser, no client.
+#
+# The Python counterpart is test_scatter.py beside it, which does the same
+# thing with shiny.testserver.test_server(). Both exist to pin this example's
+# central claim from the server side: a widget renderer produces its value
+# with no *Output() placeholder anywhere.
+#
+# Run it from the app directory, the way a user of the app would:
+#
+#   Rscript -e 'shiny::runTests()'
+#
+# The shinyreact package's own suite also runs it, via
+# pkg-r/tests/testthat/test-examples.R.
+app_dir <- testthat::test_path("..", "..")
+
+test_that("greeting counts the points", {
+  shiny::testServer(app_dir, {
+    session$setInputs(num_points = 50)
+    expect_equal(output$greeting, "Showing 50 random points")
+
+    # No singular special case.
+    session$setInputs(num_points = 1)
+    expect_equal(output$greeting, "Showing 1 random points")
+  })
+})
+
+test_that("greeting is NULL before the client's first message", {
+  # app.R returns NULL explicitly rather than using req(), so no silent error
+  # reaches the client console -- unlike `scatter`, which does use req().
+  shiny::testServer(app_dir, {
+    expect_null(output$greeting)
+  })
+})
+
+test_that("scatter renders a plotly widget with no plotlyOutput() anywhere", {
+  skip_if_not_installed("plotly")
+
+  shiny::testServer(app_dir, {
+    session$setInputs(num_points = 50)
+
+    # renderPlotly() hands the client a JSON string carrying the figure, with
+    # the widget's HTML dependencies attached as an attribute -- the React
+    # side's ShinyOutput is what mounts it, and page_react() pushes those deps
+    # after the flush.
+    expect_s3_class(output$scatter, "json")
+    expect_match(output$scatter, '"type":"scatter"', fixed = TRUE)
+    dep_names <- vapply(attr(output$scatter, "deps"), `[[`, character(1), "name")
+    expect_true("plotly-main" %in% dep_names)
+    # The *binding* JS is not in here: page_react() discovers it from the
+    # render function and pushes it as a shinyreact-deps message instead,
+    # which is what pkg-r/tests/testthat/test-dep-discovery.R covers.
+    expect_false("plotly-binding" %in% dep_names)
+  })
+})
diff --git a/examples/08-input-handler/FEATURES.md b/examples/08-input-handler/FEATURES.md
index 0053c3a5..ccab0e53 100644
--- a/examples/08-input-handler/FEATURES.md
+++ b/examples/08-input-handler/FEATURES.md
@@ -12,7 +12,9 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
 
 - the hook's `type` appends `:shiny.datetime` to the wire id, so the value
   arrives as `when:shiny.datetime` and Shiny's built-in handler coerces it
-  before `input.when()` resolves
+  before `input.when()` resolves `(test)`
+  - the suffix is what buys the coercion: the same number sent as plain `when`
+    stays an `int` `(test)`
 - opting into a `type` bypasses shinyreact's own `shinyreact.default` handler —
   the value is handled by Shiny's registry, not by shinyreact
 - the id/type pairing is a per-id contract: a second mount of `"when"` without
@@ -21,9 +23,10 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
 ## Server (`app.py`, Express)
 
 - one output, `when_info` → `"<type name> → <repr>"`, e.g.
-  `"datetime → datetime.datetime(2026, 8, 28, 12, 0, tzinfo=...)"`
-- `input.when()` is `None` before the first client message → returns `"—"`
-  (em dash)
+  `"datetime → datetime.datetime(2026, 8, 28, 12, 0, tzinfo=...)"` `(test)`
+- before the first client message, `input.when()` raises a silent exception, so
+  `when_info` never renders — the `"—"` (em dash) branch in `app.py` is
+  unreachable from a real client `(test)`
 - the example asserts nothing about the timezone the handler attaches
 - `[py]` only — this example has no R server; R's handler registry has no
   `shiny.datetime` equivalent, so the client is not portable as written
diff --git a/examples/08-input-handler/tests/test_when.py b/examples/08-input-handler/tests/test_when.py
new file mode 100644
index 00000000..fafe63aa
--- /dev/null
+++ b/examples/08-input-handler/tests/test_when.py
@@ -0,0 +1,46 @@
+"""Pins the input handler's coercion at the server, in memory.
+
+This example exists to show that `useShinyInput(..., {type: "shiny.datetime"})`
+makes the server read a `datetime`. `shiny.testserver.test_server()` can assert
+exactly that, because `set_inputs` takes the **wire** id — so the `:type`
+suffix the hook appends is part of the test, and the handler really runs. Run
+it from the app directory::
+
+    pytest
+"""
+
+from __future__ import annotations
+
+import datetime
+from pathlib import Path
+
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_the_handler_turns_unix_seconds_into_a_datetime() -> None:
+    with test_server(APP) as ts:
+        # What the client sends: unix *seconds*, under the suffixed wire id.
+        ts.set_inputs(**{"when:shiny.datetime": 1756382400})
+        echoed = ts.get_output("when_info").value
+
+        assert echoed.startswith("datetime → datetime.datetime(")
+        # The example asserts nothing about the timezone, only the type.
+        assert datetime.datetime.fromtimestamp(1756382400).year == 2025
+
+
+def test_an_unsuffixed_value_is_not_coerced() -> None:
+    # The suffix is what buys the coercion: without it the number arrives as a
+    # number. This is the failure mode the per-id type contract exists to
+    # prevent, and the reason to write the suffix out in the test above.
+    with test_server(APP) as ts:
+        ts.set_inputs(when=1756382400)
+        assert ts.get_output("when_info") == "int → 1756382400"
+
+
+def test_nothing_renders_before_the_clients_first_message() -> None:
+    # `input.when()` raises a silent exception while unset, so the `None`
+    # branch in `app.py` (the em dash) is unreachable from a real client.
+    with test_server(APP) as ts:
+        assert ts.get_output("when_info").status == "silent"
diff --git a/examples/10-bookmarking/FEATURES.md b/examples/10-bookmarking/FEATURES.md
index 0b123520..125b78d0 100644
--- a/examples/10-bookmarking/FEATURES.md
+++ b/examples/10-bookmarking/FEATURES.md
@@ -15,12 +15,16 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
     further wiring — a UI object built once could not carry a per-request
     restore payload
 - output `greeting` (`reactive_output`) → `text='<txt>' num=<num>
-  checked=<yes|no>`
-  - `checked` is the string `"yes"` / `"no"`, not a boolean
-  - `txt` is `repr`'d, so it is quoted
+  checked=<yes|no>` `(test)`
+  - `checked` is the string `"yes"` / `"no"`, not a boolean `(test)`
+  - `txt` is `repr`'d, so it is quoted `(test)`
+  - it renders from the hook defaults (`""` / `0` / `false`), since the client
+    does not gate on `useShinyInitialized()` `(test)`
 - `@reactive.effect` + `@reactive.event(input.bookmark_clicks,
   ignore_init=True)` → `await session.bookmark()`, which rewrites the browser
   URL
+  - the mount-time `0` does not bookmark; the URL rewrite itself needs a
+    browser, so in-memory tests only assert the effect runs cleanly `(test)`
 - `[py]` only — this example has no R server
 
 ## Restore path
diff --git a/examples/10-bookmarking/tests/test_greeting.py b/examples/10-bookmarking/tests/test_greeting.py
new file mode 100644
index 00000000..2fcd31e8
--- /dev/null
+++ b/examples/10-bookmarking/tests/test_greeting.py
@@ -0,0 +1,51 @@
+"""Pins the echo output and the bookmark effect's inputs.
+
+`shiny.testserver.test_server()` loads this app through `ReactApp`, so the
+server half of the example runs in memory. The *restore* half does not: it is a
+property of the rendered page and the browser URL, and stays pinned by
+`pkg-py/tests/test_bookmark_restore.py` and its Playwright counterpart. Run it
+from the app directory::
+
+    pytest
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_greeting_wire_shape() -> None:
+    with test_server(APP) as ts:
+        ts.set_inputs(txt="hi", num=5, chk=True)
+        # `checked` is the string "yes"/"no", and `txt` is repr'd, so quoted.
+        assert ts.get_output("greeting") == "text='hi' num=5 checked=yes"
+
+        ts.set_inputs(chk=False)
+        assert ts.get_output("greeting") == "text='hi' num=5 checked=no"
+
+
+def test_greeting_renders_from_the_hook_defaults() -> None:
+    # The client renders immediately rather than gating on
+    # `useShinyInitialized()`, so the first values the server sees are the
+    # hook defaults (or the restored ones).
+    with test_server(APP) as ts:
+        ts.set_inputs(txt="", num=0, chk=False)
+        assert ts.get_output("greeting") == "text='' num=0 checked=no"
+
+
+def test_a_bookmark_click_is_an_event_input() -> None:
+    # `bookmark_clicks` is write-only and `priority: "event"`, with the count
+    # incremented per click; `ignore_init=True` means the mount-time 0 does
+    # not bookmark. The URL rewrite itself needs a browser — see the
+    # Playwright suite — so all this asserts is that the effect runs cleanly.
+    with test_server(APP) as ts:
+        ts.set_inputs(txt="hi", num=5, chk=True)
+        ts.set_inputs(bookmark_clicks=0)
+        ts.set_inputs(bookmark_clicks=1)
+
+        assert ts.to_values().is_ok
+        assert ts.get_output("greeting") == "text='hi' num=5 checked=yes"
diff --git a/examples/README.md b/examples/README.md
index aa888896..937fd571 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -110,6 +110,26 @@ Rscript -e 'shiny::runTests()'           # the app's R tests (also shinytest2::t
 npx vitest run --root .. 01-hello        # the app's UI tests
 ```
 
+Most of the Python tests drive the app itself, with
+[`shiny.testserver.test_server()`](https://shiny.posit.co/py/api/testing/):
+inputs in, output values out, in memory. That is a good fit for these apps
+because a `ui.tsx` server contains only reactive computation, so the JSON a
+test asserts is exactly what `useShinyOutputValue()` receives:
+
+```python
+with test_server(APP) as ts:
+    ts.set_inputs(bins=9)
+    assert ts.get_output("dist_caption") == "272 eruptions in 9 bins"
+```
+
+Pass an absolute `Path` (`Path(__file__).resolve().parents[1] / "app.py"`), and
+mind two shinyreact-specific details: an **untyped** input id needs no
+`:shinyreact.default` suffix (the hook adds it on the wire, but Python's
+handler is a no-op), while a **typed** one does, because the suffix is what
+runs the handler; and an input read through `@reactive.event(...,
+ignore_init=True)` needs two `set_inputs` calls, mirroring the client's
+register-at-mount then send-the-event.
+
 The UI tests need a JS toolchain, which the no-build examples deliberately do
 not carry. `examples/package.json` provides one for the whole examples tree, so
 `npm install` there once covers every example:
diff --git a/pkg-py/README.md b/pkg-py/README.md
index 650ae5e6..9b6b6eea 100644
--- a/pkg-py/README.md
+++ b/pkg-py/README.md
@@ -78,6 +78,6 @@ shiny run shinyreact/examples/01-hello/app.py
 - [Get started](https://posit-dev.github.io/shinyreact/) walks through the `ui.tsx` pattern: inputs, outputs, messages, and embedding traditional Shiny renderers.
 - [TSX files and JavaScript build tools](https://posit-dev.github.io/shinyreact/articles/tsx-and-build-tools.html) explains `.tsx`, JSX, TypeScript, and what `npm run build` does.
 - [Client hooks](https://posit-dev.github.io/shinyreact/articles/hooks.html) lists everything at `window.shinyreact`.
-- [Testing wire payloads](https://posit-dev.github.io/shinyreact/articles/testing.html) covers `WireTap` for Playwright tests.
+- [Testing](https://posit-dev.github.io/shinyreact/articles/testing.html) covers `shiny.testserver.test_server()` for driving a server with no browser, and `WireTap` for wire payloads in Playwright tests.
 - [Agent Skills](https://posit-dev.github.io/shinyreact/articles/agent-skills.html) explains the skills that ship with the package for coding agents.
 - The [examples catalog](https://github.com/posit-dev/shinyreact/blob/main/examples/README.md) lists runnable apps from no-build to Vite + HMR.
diff --git a/pkg-py/docs/_quarto.yml b/pkg-py/docs/_quarto.yml
index 807c41ba..1238896b 100644
--- a/pkg-py/docs/_quarto.yml
+++ b/pkg-py/docs/_quarto.yml
@@ -97,7 +97,8 @@ quartodoc:
       contents:
         - send_message
     - title: Testing
-      desc: Record the wire payloads a Playwright test observes.
+      desc: Record the wire payloads a Playwright test observes. For testing a
+        server with no browser, see `shiny.testserver.test_server()`.
       contents:
         - playwright.WireTap
 
diff --git a/pkg-py/docs/articles/testing.qmd b/pkg-py/docs/articles/testing.qmd
index a1ef63ad..fc7527cb 100644
--- a/pkg-py/docs/articles/testing.qmd
+++ b/pkg-py/docs/articles/testing.qmd
@@ -1,13 +1,85 @@
 ---
-title: "Testing wire payloads"
+title: "Testing"
 ---
 
 In a shinyreact app the contract between server and client is the JSON that crosses the Shiny websocket: the values `reactive_output` delivers, the payloads `send_message()` pushes, and the values `useShinyInput()` sends back.
-A wire tap records those payloads in a browser test so you can assert on them directly, without inspecting the rendered DOM.
+Both halves of this page assert that JSON — the first without a browser at all, the second inside a real one.
+
+## Testing the server without a browser
+
+A `ui.tsx` server contains only reactive computation, so "this input produces that output value" *is* the server.
+Shiny can run one against a mock connection — no browser, no subprocess — and hand you the value the client would have received.
+
+::: {.panel-tabset}
+
+### Python
+
+`shiny.testserver.test_server()` loads the app file (Express or Core, `shiny.App` or `shinyreact.ReactApp`) and runs its server:
+
+```python
+from pathlib import Path
+
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_dist_outputs():
+    with test_server(APP) as ts:
+        ts.set_inputs(bins=9)
+        assert ts.get_output("dist_caption") == "272 eruptions in 9 bins"
+        assert ts.get_output("dist_data").value["counts"][0] == 16
+```
+
+`get_output()` compares equal to the underlying value, so assert on it directly; reach for `.value` to index into it, and `.status` (`"ok"`, `"error"`, `"silent"`) or `.error` for the non-value outcomes.
+Traditional renderers embedded with [`ShinyOutput`](hooks.qmd) are readable the same way, so a `@render.data_frame` payload can be checked here too.
+
+Three details are specific to shinyreact:
+
+- An **untyped** input id needs no `:shinyreact.default` suffix — the hook appends it on the wire, but Python's handler is a no-op, so `set_inputs(bins=9)` is equivalent.
+- A **typed** one does: `set_inputs(**{"when:shiny.datetime": 1756382400})` is what runs the handler and makes `input.when()` a `datetime`.
+- An **unset** input means `status == "silent"`, not a `None` value, because `input.x()` raises a silent exception while unset.
+
+An input read through `@reactive.event(..., ignore_init=True)` needs two `set_inputs` calls, mirroring the client: `useShinyInput` registers its default at mount and sends the event after.
+
+`test_server()` is newer than shiny 1.7.0.
+
+### R
+
+`reactive_output()` is an ordinary render function, so `shiny::testServer()` drives it directly and `output$id` is the JSON value itself — no spec wrapper, no coercion:
+
+```r
+test_that("dist_data bins the waiting column", {
+  shiny::testServer(app_dir, {
+    session$setInputs(bins = 9)
+    expect_named(output$dist_data, c("breaks", "counts"))
+    expect_equal(
+      unclass(output$dist_data$counts),
+      c(16L, 37L, 30L, 16L, 14L, 57L, 67L, 29L, 6L)
+    )
+    expect_equal(output$dist_caption, "272 eruptions in 9 bins")
+  })
+})
+```
+
+`unclass()` is there because the app wraps its vectors in `I()` so a one-bin result serializes as `[272]` rather than `272`; the `AsIs` class rides along on the value the test sees.
+
+Pass a directory containing the app, or the `server` function itself.
+Module ids are namespaced as the session sees them, so a scoped output is read as `` output$`counter-label` ``, or reachable through `session$makeScope("counter")`; a module server can also be driven on its own with `testServer(card_server, args = list(id = "left"), { ... })`.
+
+`testServer()` **raises** rather than reporting a status: reading an output whose render function failed `req()` throws a `shiny.silent.error`, so `expect_error(output$answer, class = "shiny.silent.error")` is how you assert an output produced nothing.
+Python's `test_server()` reports that through `.status` instead.
+
+:::
+
+## Testing wire payloads
+
+A wire tap records the payloads crossing the websocket in a browser test, so you can assert on them directly instead of inspecting the rendered DOM.
+Reserve it for what the section above structurally cannot see: the values the *client* chooses to send, real bindings, and real rendering.
 
 ::: {.panel-tabset}
 
-## Python
+### Python
 
 `shinyreact.playwright.WireTap` needs the `playwright` package.
 Construct it before `page.goto()` so it sees every frame:
@@ -23,7 +95,7 @@ def test_dist_data(page, app):
     tap.expect_output_value("dist_data", lambda d: d["breaks"][0] == 43.0)
 ```
 
-## R
+### R
 
 `wire_tap()` needs the shinytest2 package.
 Start the `AppDriver` with `shiny.trace = TRUE` so every websocket frame is recorded in the app's logs:
@@ -44,7 +116,7 @@ test_that("dist_data bins the waiting column", {
 
 :::
 
-## Matchers
+### Matchers
 
 Each `expect_*` method takes a matcher and retries until it matches or a timeout (10 seconds by default) elapses:
 
@@ -61,7 +133,7 @@ There is one `expect_*` per channel:
 
 Successive expectations on one channel assert an ordered subsequence: each scans from just past the previous match, so a value that arrives between two checks is never missed.
 
-## Full histories
+### Full histories
 
 `all_output_values(id)`, `all_messages(id)`, and `all_input_values(id)` return everything that crossed a channel, in order.
 Input ids match the bare id or any `id:type` wire id, so use the id you wrote in `useShinyInput()`.
diff --git a/pkg-py/src/shinyreact/.agents/skills/shinyreact-build-app/SKILL.md b/pkg-py/src/shinyreact/.agents/skills/shinyreact-build-app/SKILL.md
index 0a922ace..0a225bee 100644
--- a/pkg-py/src/shinyreact/.agents/skills/shinyreact-build-app/SKILL.md
+++ b/pkg-py/src/shinyreact/.agents/skills/shinyreact-build-app/SKILL.md
@@ -383,8 +383,8 @@ a list. Use `type: "shinyreact.asis"` for the parsed value untouched.
 Do not stop at "the code is written". Three steps, in order:
 
 1. **Factor pure logic out of the app file** — binning, formatting,
-   conversions go in a module beside the app. Logic inside `app.py` /
-   `app.R` next to the page call cannot be reached by a test at all.
+   conversions go in a module beside the app, where a test can import them
+   without starting a session at all.
 2. **Write down what the app does, in plain English, before the tests.** An
    agent that writes the client and then writes the client's tests is
    agreeing with itself — both encode the same misunderstanding. A
@@ -394,16 +394,19 @@ Do not stop at "the code is written". Three steps, in order:
    directory** — `pytest`, or `[r]` `shiny::runTests()`, which needs the
    `tests/testthat.R` + `tests/testthat/` layout.
 
-`[r]` `shiny::testServer()` drives the reactive graph with no browser:
-`session$setInputs(bins = 9)` then assert on `output$dist_data`, which is the
-JSON value the client would have received. **`[py]` has no equivalent**, so
-factoring logic into an importable module matters more there.
+Both languages drive the reactive graph with no browser, which for a `ui.tsx`
+app is most of the server: `[r]` `shiny::testServer()` (`session$setInputs(bins
+= 9)`, then assert on `output$dist_data`) and `[py]`
+`shiny.testserver.test_server()` (`ts.set_inputs(bins=9)`, then
+`ts.get_output("dist_data")`). Either way the value you assert is the JSON the
+client would have received.
 
 [`references/testing.md`](references/testing.md) has the four layers, the test
-layout for each language, `testServer()` for plain and module servers, how to
-mount the real `www/ui.js` against a fake Shiny, and the traps that cost time
-(React ignores raw `change` events; debounce coalesces within a tick even at
-`debounceMs: 0`).
+layout for each language, `testServer()` / `test_server()` for plain and module
+servers — including the input ids that need a `:type` suffix and the event
+inputs that need two `set_inputs` calls — how to mount the real `www/ui.js`
+against a fake Shiny, and the traps that cost time (React ignores raw `change`
+events; debounce coalesces within a tick even at `debounceMs: 0`).
 
 ## Debugging
 
diff --git a/pkg-py/src/shinyreact/.agents/skills/shinyreact-build-app/references/testing.md b/pkg-py/src/shinyreact/.agents/skills/shinyreact-build-app/references/testing.md
index 8fa6e978..245ede5e 100644
--- a/pkg-py/src/shinyreact/.agents/skills/shinyreact-build-app/references/testing.md
+++ b/pkg-py/src/shinyreact/.agents/skills/shinyreact-build-app/references/testing.md
@@ -3,8 +3,11 @@
 Do not stop at "the code is written". At minimum:
 
 1. **Factor pure logic out of the app file.** Binning, formatting, conversions
-   go in a module beside the app so a test can import them; logic sitting
-   inside `app.py` / `app.R` next to the page call cannot be reached at all.
+   go in a module beside the app so a test can import them directly, with no
+   session at all. Logic left inside `app.py` / `app.R` next to the page call
+   is still reachable — `testServer()` / `test_server()` below drive the app
+   itself — but only through an input, which is a slower and blunter tool than
+   calling a function.
 2. **Write down what the app does, in plain English, before the tests** — a
    behavior file beside the app, one atomically checkable claim per line
    ("the caption reads `N eruptions in M bins`, singular `bin` at M=1"). An
@@ -16,7 +19,7 @@ Do not stop at "the code is written". At minimum:
 | Layer | Proves | Cost |
 |---|---|---|
 | pure functions in their own module | binning, formatting, conversions | trivial — always do this |
-| `[r]` `shiny::testServer()` | the reactive graph: inputs in, `reactive_output` values out | low, and no browser |
+| `shiny::testServer()` `[r]` / `shiny.testserver.test_server()` `[py]` | the reactive graph: inputs in, `reactive_output` values out | low, and no browser |
 | the client mounted in jsdom against a fake Shiny | rendering, input wiring, wire ids, status handling | low, and it exercises the file the app ships |
 | Playwright | layout, real Shiny, real bindings | high; reserve for what the others cannot see |
 
@@ -31,7 +34,8 @@ myapp/
   faithful.py            the factored logic
   www/ui.js
   tests/
-    test_faithful.py     [py]  pytest
+    test_faithful.py     [py]  pytest — the factored logic, called directly
+    test_outputs.py      [py]  pytest — the app, via test_server()
     testthat.R           [r]   runner: library(testthat); test_dir("testthat")
     testthat/
       test-histogram.R   [r]
@@ -58,11 +62,17 @@ sys.path.insert(0, str(EXAMPLE))
 from faithful import histogram, waiting  # noqa: E402
 ```
 
-## `[r]` Testing the server with `testServer()`
+## Testing the server: `testServer()` `[r]`, `test_server()` `[py]`
 
-`reactive_output` is an ordinary Shiny render function, so `shiny::testServer()`
-drives it with no browser and no client: set inputs, read outputs, and get the
-JSON value the client would have received.
+**This is the highest-value layer for a `ui.tsx` app.** The server contains
+only reactive computation, so "input X produces output Y" *is* the server, and
+both languages can assert it with no browser and no client: set inputs, read
+outputs, and get the JSON value the client would have received.
+
+### `[r]` `shiny::testServer()`
+
+`reactive_output` is an ordinary Shiny render function, so `testServer()`
+drives it directly.
 
 ```r
 test_that("the histogram recomputes when bins changes", {
@@ -90,10 +100,62 @@ which is most of what a shinyreact server does.
 Module servers work the same way: `testServer(card_server, args = list(id =
 "left"), { ... })`.
 
-**`[py]` has no `testServer()` equivalent.** Cover the Python server by
-factoring its logic into a module and testing that with pytest, and let the
-jsdom and Playwright layers cover the wiring. This is a real gap, not an
-oversight in your app.
+### `[py]` `shiny.testserver.test_server()`
+
+The Python counterpart (py-shiny#2470, so newer than shiny 1.7.0). It loads the
+app file — Express or Core, `shiny.App` or `shinyreact.ReactApp` — and runs its
+server against a mock connection:
+
+```python
+from pathlib import Path
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_the_histogram_recomputes_when_bins_changes():
+    with test_server(APP) as ts:
+        ts.set_inputs(bins=9)
+        assert ts.get_output("dist_data").value["counts"] == [16, 37, 30, 16, 14, 57, 67, 29, 6]
+        assert ts.get_output("dist_caption") == "272 eruptions in 9 bins"
+```
+
+`get_output()` returns a value that compares equal to the underlying one, so
+assert on it directly; use `.value` when you need to index into it, and
+`.status` (`"ok"` / `"error"` / `"silent"`) or `.error` to assert the
+non-value outcomes. Traditional renderers are readable too, so
+`@render.data_frame` / `@render_plotly` outputs mounted through `ShinyOutput`
+can be checked at the wire level.
+
+Pass an **absolute `Path`**: a relative one resolves against the test file's
+directory, and the app is a directory up from `tests/`.
+
+Four things to know, all of them shinyreact-specific:
+
+- **An untyped input id needs no `:shinyreact.default` suffix.** The hook
+  appends it on the wire, but both Python handlers are no-ops, so
+  `set_inputs(bins=9)` is equivalent.
+- **A typed one does.** `set_inputs(**{"when:shiny.datetime": 1756382400})` is
+  what makes the handler run and `input.when()` a `datetime`; without the
+  suffix you are testing a different app than the one the client drives.
+- **An event input needs two calls.** `useShinyInput` registers its default at
+  mount and sends the event after, so an output behind
+  `@reactive.event(..., ignore_init=True)` only fires on the *second*
+  `set_inputs` for that id.
+- **An unset input means `status == "silent"`, not a `None` value.**
+  `input.x()` raises a silent exception while unset, so a `if x is None:`
+  branch in your server is unreachable from a real client — assert the status
+  instead. (A *later* `req()` failure is not visible in memory at all:
+  py-shiny#2492.)
+
+Module ids can be read as the session sees them (`ts.get_output("counter-n")`)
+or through a scope, which strips the namespace on the way in and out:
+
+```python
+with ts.make_scope("counter") as counter:
+    counter.set_inputs(n=7)
+    assert counter.get_output("label") == "n=7"
+```
 
 ## The jsdom layer — mount the client the app ships
 
diff --git a/pkg-py/src/shinyreact/.agents/skills/shinyreact-convert-app/SKILL.md b/pkg-py/src/shinyreact/.agents/skills/shinyreact-convert-app/SKILL.md
index ed308117..c8184922 100644
--- a/pkg-py/src/shinyreact/.agents/skills/shinyreact-convert-app/SKILL.md
+++ b/pkg-py/src/shinyreact/.agents/skills/shinyreact-convert-app/SKILL.md
@@ -149,12 +149,16 @@ rendered), then the rest of the outputs, then layout and polish.
 
 ## Phase 5 — verify
 
-Three layers, cheapest first: factor pure logic out of the app file so it is
-importable and test it directly; test the client by evaluating the real
-`www/ui.js` against a fake `window.Shiny` in jsdom (not by importing the
-component — that tests a copy the app does not ship); and reserve Playwright
-for layout and real bindings, which the other two structurally cannot see. The
-`shinyreact-build-app` skill's `references/testing.md` has the traps.
+Four layers, cheapest first: factor pure logic out of the app file so it is
+importable and test it directly; drive the ported server with no browser —
+`[r]` `shiny::testServer()`, `[py]` `shiny.testserver.test_server()` — which
+for a `ui.tsx` app covers most of it, since the server is only reactive
+computation; test the client by evaluating the real `www/ui.js` against a fake
+`window.Shiny` in jsdom (not by importing the component — that tests a copy the
+app does not ship); and reserve Playwright for layout and real bindings, which
+the others structurally cannot see. The `shinyreact-build-app` skill's
+[`references/testing.md`](../shinyreact-build-app/references/testing.md) has
+the details and the traps.
 
 A port has one advantage a new app does not: **the original still runs.** Where
 the logic is a pure transform, capture its output from the original app and
diff --git a/pkg-py/tests/test_in_memory_server.py b/pkg-py/tests/test_in_memory_server.py
new file mode 100644
index 00000000..595efe28
--- /dev/null
+++ b/pkg-py/tests/test_in_memory_server.py
@@ -0,0 +1,92 @@
+"""Server-side behavior of the ui.tsx pattern, driven in memory.
+
+`shiny.testserver.test_server()` (py-shiny#2470) runs an app's server function
+against a mock connection: inputs in, output values out, no browser and no
+subprocess. That suits shinyreact particularly well — a ui.tsx server is *only*
+reactive computation, so what a test wants to assert is the JSON that reaches
+`useShinyOutputValue()`, which is exactly what `get_output()` hands back.
+
+The apps here are the Playwright fixture apps, reused as-is: these tests pin
+the server half of claims whose client half still needs a browser (see
+`pkg-py/tests/playwright/`). `test_server` needs no `tests-e2e` extras, so this
+file lives in the unit suite.
+
+Two shinyreact-specific notes for anyone adding to this file:
+
+- **Untyped input ids need no `:shinyreact.default` suffix.** The React hook
+  appends it on the wire, but both Python handlers are no-ops, so
+  `set_inputs(n=1)` and `set_inputs(**{"n:shinyreact.default": 1})` reach the
+  server identically. Use the suffixed form only when the handler itself is
+  what you are testing (see `test_input_handler_dispatch.py`).
+- **Event inputs need two calls.** A client registers a `useShinyInput`
+  default at mount and sends the event after, so an output guarded by
+  `@reactive.event(..., ignore_init=True)` only fires on the *second*
+  `set_inputs` for that id.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from shiny.testserver import test_server
+
+APPS = Path(__file__).parent / "playwright" / "apps"
+
+
+def test_reactive_output_publishes_raw_json() -> None:
+    """The value a `reactive_output` returns reaches the client unwrapped.
+
+    `test_reactive_output.py` asserts this through `Renderer.transform()`;
+    here it goes through a real session, so nothing between the render function
+    and the wire can re-wrap it.
+    """
+    with test_server(APPS / "module_counter" / "app.py") as ts:
+        ts.set_inputs(**{"a-count": 3})
+        assert ts.get_output("a-serverCount") == 3
+
+
+def test_module_namespaces_stay_isolated() -> None:
+    """In-memory twin of `playwright/test_module_namespaces.py`.
+
+    A scope is the test-side counterpart of the `SessionProxy` a module server
+    receives, so the module's ids can be read bare.
+    """
+    with test_server(APPS / "module_counter" / "app.py") as ts:
+        with ts.make_scope("a") as a:
+            a.set_inputs(count=2)
+            assert a.get_output("serverCount") == 2
+
+        # Namespace isolation: counter "b" is untouched, and its output has not
+        # rendered at all.
+        assert ts.get_output("b-serverCount").status == "silent"
+        assert ts.get_output("a-serverCount") == 2
+
+
+def test_output_error_statuses() -> None:
+    """Server half of `playwright/test_output_error.py`.
+
+    Which of the three outcomes an input produces — a value, a silent
+    `req()`, or an error message — is decided server-side; only the rendering
+    of each needs the browser.
+    """
+    with test_server(APPS / "output-error" / "app.py") as ts:
+        ts.set_inputs(n=1)
+        assert ts.get_output("answer") == "ok: 1"
+        assert ts.get_output("answer").status == "ok"
+
+        # A *silent* req() failure is invisible in memory: real Shiny sends a
+        # null value that blanks the output (asserted in the e2e test), but
+        # `test_server` leaves the previous value recorded, so `status` stays
+        # "ok" with the stale "ok: 1". "silent" means "never rendered", not
+        # "rendered nothing this time" — don't assert silence here.
+        ts.set_inputs(n=-1)
+        assert ts.get_output("answer") == "ok: 1"
+
+        ts.set_inputs(n=0)
+        assert ts.get_output("answer").status == "error"
+        assert ts.get_output("answer").error == "invalid number of 'breaks'"
+
+        # Recovering clears the error.
+        ts.set_inputs(n=2)
+        assert ts.get_output("answer") == "ok: 2"
+        assert ts.get_output("answer").error is None
diff --git a/pkg-r/README.md b/pkg-r/README.md
index 0914a16f..2df1456b 100644
--- a/pkg-r/README.md
+++ b/pkg-r/README.md
@@ -63,6 +63,6 @@ shiny::runGitHub("posit-dev/shinyreact", subdir = "examples/01-hello")
 
 - `vignette("shinyreact")` walks through the `ui.tsx` pattern: inputs, outputs, messages, and embedding traditional Shiny renderers.
 - [TSX files and JavaScript build tools](https://posit-dev.github.io/shinyreact/articles/tsx-and-build-tools.html) explains `.tsx`, JSX, TypeScript, and what `npm run build` does.
-- [Testing wire payloads](https://posit-dev.github.io/shinyreact/r/articles/testing.html) covers `wire_tap()` for shinytest2 tests.
+- [Testing](https://posit-dev.github.io/shinyreact/r/articles/testing.html) covers `shiny::testServer()` for driving a server with no browser, and `wire_tap()` for wire payloads in shinytest2 tests.
 - [Agent Skills](https://posit-dev.github.io/shinyreact/r/articles/agent-skills.html) explains the skills that ship with the package for coding agents.
 - The [examples catalog](https://github.com/posit-dev/shinyreact/blob/main/examples/README.md) lists runnable apps from no-build to Vite + HMR.
diff --git a/pkg-r/inst/skills/shinyreact-build-app/SKILL.md b/pkg-r/inst/skills/shinyreact-build-app/SKILL.md
index 0a922ace..0a225bee 100644
--- a/pkg-r/inst/skills/shinyreact-build-app/SKILL.md
+++ b/pkg-r/inst/skills/shinyreact-build-app/SKILL.md
@@ -383,8 +383,8 @@ a list. Use `type: "shinyreact.asis"` for the parsed value untouched.
 Do not stop at "the code is written". Three steps, in order:
 
 1. **Factor pure logic out of the app file** — binning, formatting,
-   conversions go in a module beside the app. Logic inside `app.py` /
-   `app.R` next to the page call cannot be reached by a test at all.
+   conversions go in a module beside the app, where a test can import them
+   without starting a session at all.
 2. **Write down what the app does, in plain English, before the tests.** An
    agent that writes the client and then writes the client's tests is
    agreeing with itself — both encode the same misunderstanding. A
@@ -394,16 +394,19 @@ Do not stop at "the code is written". Three steps, in order:
    directory** — `pytest`, or `[r]` `shiny::runTests()`, which needs the
    `tests/testthat.R` + `tests/testthat/` layout.
 
-`[r]` `shiny::testServer()` drives the reactive graph with no browser:
-`session$setInputs(bins = 9)` then assert on `output$dist_data`, which is the
-JSON value the client would have received. **`[py]` has no equivalent**, so
-factoring logic into an importable module matters more there.
+Both languages drive the reactive graph with no browser, which for a `ui.tsx`
+app is most of the server: `[r]` `shiny::testServer()` (`session$setInputs(bins
+= 9)`, then assert on `output$dist_data`) and `[py]`
+`shiny.testserver.test_server()` (`ts.set_inputs(bins=9)`, then
+`ts.get_output("dist_data")`). Either way the value you assert is the JSON the
+client would have received.
 
 [`references/testing.md`](references/testing.md) has the four layers, the test
-layout for each language, `testServer()` for plain and module servers, how to
-mount the real `www/ui.js` against a fake Shiny, and the traps that cost time
-(React ignores raw `change` events; debounce coalesces within a tick even at
-`debounceMs: 0`).
+layout for each language, `testServer()` / `test_server()` for plain and module
+servers — including the input ids that need a `:type` suffix and the event
+inputs that need two `set_inputs` calls — how to mount the real `www/ui.js`
+against a fake Shiny, and the traps that cost time (React ignores raw `change`
+events; debounce coalesces within a tick even at `debounceMs: 0`).
 
 ## Debugging
 
diff --git a/pkg-r/inst/skills/shinyreact-build-app/references/testing.md b/pkg-r/inst/skills/shinyreact-build-app/references/testing.md
index 8fa6e978..245ede5e 100644
--- a/pkg-r/inst/skills/shinyreact-build-app/references/testing.md
+++ b/pkg-r/inst/skills/shinyreact-build-app/references/testing.md
@@ -3,8 +3,11 @@
 Do not stop at "the code is written". At minimum:
 
 1. **Factor pure logic out of the app file.** Binning, formatting, conversions
-   go in a module beside the app so a test can import them; logic sitting
-   inside `app.py` / `app.R` next to the page call cannot be reached at all.
+   go in a module beside the app so a test can import them directly, with no
+   session at all. Logic left inside `app.py` / `app.R` next to the page call
+   is still reachable — `testServer()` / `test_server()` below drive the app
+   itself — but only through an input, which is a slower and blunter tool than
+   calling a function.
 2. **Write down what the app does, in plain English, before the tests** — a
    behavior file beside the app, one atomically checkable claim per line
    ("the caption reads `N eruptions in M bins`, singular `bin` at M=1"). An
@@ -16,7 +19,7 @@ Do not stop at "the code is written". At minimum:
 | Layer | Proves | Cost |
 |---|---|---|
 | pure functions in their own module | binning, formatting, conversions | trivial — always do this |
-| `[r]` `shiny::testServer()` | the reactive graph: inputs in, `reactive_output` values out | low, and no browser |
+| `shiny::testServer()` `[r]` / `shiny.testserver.test_server()` `[py]` | the reactive graph: inputs in, `reactive_output` values out | low, and no browser |
 | the client mounted in jsdom against a fake Shiny | rendering, input wiring, wire ids, status handling | low, and it exercises the file the app ships |
 | Playwright | layout, real Shiny, real bindings | high; reserve for what the others cannot see |
 
@@ -31,7 +34,8 @@ myapp/
   faithful.py            the factored logic
   www/ui.js
   tests/
-    test_faithful.py     [py]  pytest
+    test_faithful.py     [py]  pytest — the factored logic, called directly
+    test_outputs.py      [py]  pytest — the app, via test_server()
     testthat.R           [r]   runner: library(testthat); test_dir("testthat")
     testthat/
       test-histogram.R   [r]
@@ -58,11 +62,17 @@ sys.path.insert(0, str(EXAMPLE))
 from faithful import histogram, waiting  # noqa: E402
 ```
 
-## `[r]` Testing the server with `testServer()`
+## Testing the server: `testServer()` `[r]`, `test_server()` `[py]`
 
-`reactive_output` is an ordinary Shiny render function, so `shiny::testServer()`
-drives it with no browser and no client: set inputs, read outputs, and get the
-JSON value the client would have received.
+**This is the highest-value layer for a `ui.tsx` app.** The server contains
+only reactive computation, so "input X produces output Y" *is* the server, and
+both languages can assert it with no browser and no client: set inputs, read
+outputs, and get the JSON value the client would have received.
+
+### `[r]` `shiny::testServer()`
+
+`reactive_output` is an ordinary Shiny render function, so `testServer()`
+drives it directly.
 
 ```r
 test_that("the histogram recomputes when bins changes", {
@@ -90,10 +100,62 @@ which is most of what a shinyreact server does.
 Module servers work the same way: `testServer(card_server, args = list(id =
 "left"), { ... })`.
 
-**`[py]` has no `testServer()` equivalent.** Cover the Python server by
-factoring its logic into a module and testing that with pytest, and let the
-jsdom and Playwright layers cover the wiring. This is a real gap, not an
-oversight in your app.
+### `[py]` `shiny.testserver.test_server()`
+
+The Python counterpart (py-shiny#2470, so newer than shiny 1.7.0). It loads the
+app file — Express or Core, `shiny.App` or `shinyreact.ReactApp` — and runs its
+server against a mock connection:
+
+```python
+from pathlib import Path
+from shiny.testserver import test_server
+
+APP = Path(__file__).resolve().parents[1] / "app.py"
+
+
+def test_the_histogram_recomputes_when_bins_changes():
+    with test_server(APP) as ts:
+        ts.set_inputs(bins=9)
+        assert ts.get_output("dist_data").value["counts"] == [16, 37, 30, 16, 14, 57, 67, 29, 6]
+        assert ts.get_output("dist_caption") == "272 eruptions in 9 bins"
+```
+
+`get_output()` returns a value that compares equal to the underlying one, so
+assert on it directly; use `.value` when you need to index into it, and
+`.status` (`"ok"` / `"error"` / `"silent"`) or `.error` to assert the
+non-value outcomes. Traditional renderers are readable too, so
+`@render.data_frame` / `@render_plotly` outputs mounted through `ShinyOutput`
+can be checked at the wire level.
+
+Pass an **absolute `Path`**: a relative one resolves against the test file's
+directory, and the app is a directory up from `tests/`.
+
+Four things to know, all of them shinyreact-specific:
+
+- **An untyped input id needs no `:shinyreact.default` suffix.** The hook
+  appends it on the wire, but both Python handlers are no-ops, so
+  `set_inputs(bins=9)` is equivalent.
+- **A typed one does.** `set_inputs(**{"when:shiny.datetime": 1756382400})` is
+  what makes the handler run and `input.when()` a `datetime`; without the
+  suffix you are testing a different app than the one the client drives.
+- **An event input needs two calls.** `useShinyInput` registers its default at
+  mount and sends the event after, so an output behind
+  `@reactive.event(..., ignore_init=True)` only fires on the *second*
+  `set_inputs` for that id.
+- **An unset input means `status == "silent"`, not a `None` value.**
+  `input.x()` raises a silent exception while unset, so a `if x is None:`
+  branch in your server is unreachable from a real client — assert the status
+  instead. (A *later* `req()` failure is not visible in memory at all:
+  py-shiny#2492.)
+
+Module ids can be read as the session sees them (`ts.get_output("counter-n")`)
+or through a scope, which strips the namespace on the way in and out:
+
+```python
+with ts.make_scope("counter") as counter:
+    counter.set_inputs(n=7)
+    assert counter.get_output("label") == "n=7"
+```
 
 ## The jsdom layer — mount the client the app ships
 
diff --git a/pkg-r/inst/skills/shinyreact-convert-app/SKILL.md b/pkg-r/inst/skills/shinyreact-convert-app/SKILL.md
index ed308117..c8184922 100644
--- a/pkg-r/inst/skills/shinyreact-convert-app/SKILL.md
+++ b/pkg-r/inst/skills/shinyreact-convert-app/SKILL.md
@@ -149,12 +149,16 @@ rendered), then the rest of the outputs, then layout and polish.
 
 ## Phase 5 — verify
 
-Three layers, cheapest first: factor pure logic out of the app file so it is
-importable and test it directly; test the client by evaluating the real
-`www/ui.js` against a fake `window.Shiny` in jsdom (not by importing the
-component — that tests a copy the app does not ship); and reserve Playwright
-for layout and real bindings, which the other two structurally cannot see. The
-`shinyreact-build-app` skill's `references/testing.md` has the traps.
+Four layers, cheapest first: factor pure logic out of the app file so it is
+importable and test it directly; drive the ported server with no browser —
+`[r]` `shiny::testServer()`, `[py]` `shiny.testserver.test_server()` — which
+for a `ui.tsx` app covers most of it, since the server is only reactive
+computation; test the client by evaluating the real `www/ui.js` against a fake
+`window.Shiny` in jsdom (not by importing the component — that tests a copy the
+app does not ship); and reserve Playwright for layout and real bindings, which
+the others structurally cannot see. The `shinyreact-build-app` skill's
+[`references/testing.md`](../shinyreact-build-app/references/testing.md) has
+the details and the traps.
 
 A port has one advantage a new app does not: **the original still runs.** Where
 the logic is a pure transform, capture its output from the original app and
diff --git a/pkg-r/tests/testthat/test-examples.R b/pkg-r/tests/testthat/test-examples.R
index 4d4e3498..c57bb728 100644
--- a/pkg-r/tests/testthat/test-examples.R
+++ b/pkg-r/tests/testthat/test-examples.R
@@ -44,8 +44,18 @@ test_that("R example apps are installed at examples-shiny/<name>", {
 test_that("shipped R example apps match examples/", {
   skip_if_not(dir.exists(examples_dir), "not running from the repo")
 
+  # Only app.R + www/ are copied; the example's README/FEATURES/tests and its
+  # Python siblings stay in examples/. Filter before reading, not after: the
+  # example directories also hold binary files (__pycache__, node_modules)
+  # that readLines() warns about.
+  copied <- "^(app\\.R|www/)"
+
   tree <- function(root) {
-    files <- sort(list.files(root, recursive = TRUE))
+    files <- sort(grep(
+      copied,
+      list.files(root, recursive = TRUE),
+      value = TRUE
+    ))
     stats::setNames(
       lapply(files, function(f) readLines(file.path(root, f))),
       files
@@ -53,10 +63,7 @@ test_that("shipped R example apps match examples/", {
   }
 
   for (name in shipped_r_examples) {
-    # Only app.R + www/ are copied; the example's README/FEATURES/tests and its
-    # Python siblings stay in examples/.
     src <- tree(file.path(examples_dir, name))
-    src <- src[grepl("^(app\\.R|www/)", names(src))]
     expect_equal(
       tree(system.file("examples-shiny", name, package = "shinyreact")),
       src,
diff --git a/pkg-r/tests/testthat/test-render.R b/pkg-r/tests/testthat/test-render.R
index c96bc645..0bffdcc6 100644
--- a/pkg-r/tests/testthat/test-render.R
+++ b/pkg-r/tests/testthat/test-render.R
@@ -49,3 +49,70 @@ test_that("reactive_output attaches no UI placeholder or dependency", {
   expect_no_match(placeholder$html, "my_id", fixed = TRUE)
   expect_length(placeholder$dependencies, 0L)
 })
+
+test_that("reactive_output is namespaced inside a module server", {
+  # Mirrors test_module_namespaces_stay_isolated in
+  # pkg-py/tests/test_in_memory_server.py, which drives the same app shape
+  # through shiny.testserver.test_server(). The browser-level counterpart is
+  # pkg-py/tests/playwright/test_module_namespaces.py; R has no e2e suite yet
+  # (#194), so this is R's coverage of the claim.
+  counter_server <- function(id) {
+    moduleServer(id, function(input, output, session) {
+      output$serverCount <- reactive_output(
+        if (is.null(input$count)) 0L else input$count
+      )
+    })
+  }
+  server <- function(input, output, session) {
+    counter_server("a")
+    counter_server("b")
+  }
+
+  shiny::testServer(server, {
+    session$setInputs(`a-count` = 3L)
+    expect_identical(output$`a-serverCount`, 3L)
+    # Namespace isolation: counter "b" is untouched.
+    expect_identical(output$`b-serverCount`, 0L)
+  })
+
+  # The same ids through a scope, which is how a module's own test reads them.
+  shiny::testServer(server, {
+    a <- session$makeScope("a")
+    a$setInputs(count = 2L)
+    expect_identical(output$`a-serverCount`, 2L)
+  })
+})
+
+test_that("reactive_output surfaces errors and silent errors to the test", {
+  # Mirrors test_output_error_statuses in pkg-py/tests/test_in_memory_server.py
+  # -- with a deliberate divergence in the *testing* API, not in shinyreact:
+  # R's testServer() re-raises, so reading the output is the assertion, while
+  # Python's test_server() reports `.status` / `.error` instead. Python also
+  # keeps the previous value after a silent error where R does not
+  # (posit-dev/py-shiny#2492).
+  server <- function(input, output, session) {
+    output$answer <- reactive_output({
+      n <- input$n
+      req(!is.null(n))
+      if (n == 0) {
+        stop("invalid number of 'breaks'")
+      }
+      paste0("ok: ", n)
+    })
+  }
+
+  shiny::testServer(server, {
+    # req() fails: a silent error, with no message.
+    expect_error(output$answer, class = "shiny.silent.error")
+
+    session$setInputs(n = 1)
+    expect_identical(output$answer, "ok: 1")
+
+    session$setInputs(n = 0)
+    expect_error(output$answer, "invalid number of 'breaks'")
+
+    # Recovering clears the error.
+    session$setInputs(n = 2)
+    expect_identical(output$answer, "ok: 2")
+  })
+})
diff --git a/pkg-r/vignettes/articles/testing.Rmd b/pkg-r/vignettes/articles/testing.Rmd
index d3c51918..1f72857e 100644
--- a/pkg-r/vignettes/articles/testing.Rmd
+++ b/pkg-r/vignettes/articles/testing.Rmd
@@ -1,5 +1,5 @@
 ---
-title: "Testing wire payloads"
+title: "Testing"
 ---
 
 ```{r, include = FALSE}
@@ -9,11 +9,71 @@ knitr::opts_chunk$set(collapse = TRUE, comment = "#>", eval = FALSE)
 In a shinyreact app the contract between server and client is the JSON that
 crosses the Shiny websocket: the values `reactive_output()` delivers, the
 payloads `send_message()` pushes, and the values `useShinyInput()` sends back.
-`wire_tap()` records those payloads in a
+Both halves of this article assert that JSON — the first with no browser at
+all, the second inside a real one.
+
+## Testing the server with `testServer()`
+
+A `ui.tsx` server contains only reactive computation, so "this input produces
+that output value" *is* the server. `reactive_output()` is an ordinary render
+function, so `shiny::testServer()` drives it with no browser and no client, and
+`output$id` is the JSON value itself — no spec wrapper, no coercion:
+
+```{r}
+test_that("dist_data bins the waiting column", {
+  shiny::testServer(app_dir, {
+    session$setInputs(bins = 9)
+
+    expect_named(output$dist_data, c("breaks", "counts"))
+    expect_equal(
+      unclass(output$dist_data$counts),
+      c(16L, 37L, 30L, 16L, 14L, 57L, 67L, 29L, 6L)
+    )
+    expect_equal(output$dist_caption, "272 eruptions in 9 bins")
+  })
+})
+```
+
+`unclass()` is there because the app wraps its vectors in `I()` so a one-bin
+result serializes as `[272]` rather than `272` — the `AsIs` class rides along
+on the value the test sees.
+
+Pass a directory containing the app, or the `server` function itself. Module
+ids are namespaced as the session sees them (``output$`counter-label` ``), or
+reachable through `session$makeScope("counter")`; a module server can also be
+driven on its own:
+
+```{r}
+shiny::testServer(card_server, args = list(id = "left"), {
+  session$setInputs(n = 7)
+  expect_equal(output$label, "n=7")
+})
+```
+
+`testServer()` **raises** rather than reporting a status. Reading an output
+whose render function failed `req()` throws a silent error, which is how you
+assert that an output produced nothing:
+
+```{r}
+expect_error(output$answer, class = "shiny.silent.error")
+```
+
+`examples/01-hello` and `examples/07-plotly` both carry a
+`tests/testthat/test-outputs.R` written this way, runnable from the app
+directory with `shiny::runTests()`.
+
+The Python counterpart is `shiny.testserver.test_server()`, which reports
+`.status` (`"ok"`, `"error"`, `"silent"`) instead of raising.
+
+## Testing wire payloads with `wire_tap()`
+
+`wire_tap()` records the payloads crossing the websocket in a
 [shinytest2](https://rstudio.github.io/shinytest2/) test so you can assert on
-them directly, without inspecting the rendered DOM.
+them directly, without inspecting the rendered DOM. Reserve it for what
+`testServer()` structurally cannot see: the values the *client* chooses to
+send, real bindings, and real rendering.
 
-## Setup
+### Setup
 
 `wire_tap()` needs the shinytest2 package. Start the `AppDriver` with
 `shiny.trace = TRUE` so every websocket frame is recorded in the app's logs:
@@ -32,7 +92,7 @@ test_that("dist_data bins the waiting column", {
 })
 ```
 
-## Matchers
+### Matchers
 
 Each `expect_*` function takes a matcher and retries until it matches or a
 timeout (10 seconds by default) elapses:
@@ -54,7 +114,7 @@ Successive expectations on one channel assert an ordered subsequence: each
 scans from just past the previous match, so a value that arrives between two
 checks is never missed.
 
-## Full histories
+### Full histories
 
 To inspect everything that crossed a channel, use the `all_*` functions:
 
@@ -67,7 +127,7 @@ tap$all_input_values("bins")
 Input ids match the bare id or any `id:type` wire id, so use the id you wrote
 in `useShinyInput()`.
 
-## Python counterpart
+### Python counterpart
 
 `shinyreact.playwright.WireTap` in the Python package has the same methods and
 semantics for Playwright tests. One divergence: `jsonlite::fromJSON()` maps a
diff --git a/pkg-r/vignettes/shinyreact.Rmd b/pkg-r/vignettes/shinyreact.Rmd
index bd2a3943..af07f8be 100644
--- a/pkg-r/vignettes/shinyreact.Rmd
+++ b/pkg-r/vignettes/shinyreact.Rmd
@@ -189,8 +189,9 @@ them as initial values instead of its default.
 - [TSX files and JavaScript build tools](https://posit-dev.github.io/shinyreact/articles/tsx-and-build-tools.html)
   explains `.tsx`, JSX, TypeScript, and what `npm run build` does, for
   readers new to JavaScript tooling.
-- [Testing wire payloads](https://posit-dev.github.io/shinyreact/r/articles/testing.html)
-  shows how to assert the JSON that crosses the websocket with `wire_tap()`.
+- [Testing](https://posit-dev.github.io/shinyreact/r/articles/testing.html)
+  shows how to assert the JSON a server produces with `shiny::testServer()`,
+  and the JSON that crosses the websocket with `wire_tap()`.
 - The [JS reference](https://posit-dev.github.io/shinyreact/js/) documents
   every hook and component at `window.shinyreact`.
 - [`DESIGN.md`](https://github.com/posit-dev/shinyreact/blob/main/DESIGN.md)

From 9dfa818f0fd925cb4e7ffc3075627523b30701a7 Mon Sep 17 00:00:00 2001
From: Barret Schloerke <barret@posit.co>
Date: Fri, 11 Sep 2026 17:02:05 -0400
Subject: [PATCH 2/3] docs(examples): say why 11-npm-local's server leaves
 carry no (test)

Merging main brought in a new example. Its tests deliberately never load the
app -- in Python that would trigger its build-on-first-run -- so test_server()
is out of reach there, which is worth a leaf rather than a silent gap.
---
 examples/11-npm-local/FEATURES.md | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/examples/11-npm-local/FEATURES.md b/examples/11-npm-local/FEATURES.md
index 135a535b..6c401f5f 100644
--- a/examples/11-npm-local/FEATURES.md
+++ b/examples/11-npm-local/FEATURES.md
@@ -57,6 +57,11 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
   - `[py]` `input.bins()` raises a silent exception, so neither output produces
     a value
   - `[r]` `input$bins` is `NULL` and both outputs return `NULL` explicitly
+- alone among the examples, the outputs are **not** driven in memory:
+  `test_server()` / `testServer()` load the app, which is the one thing this
+  example's tests avoid — `[py]` loading `app.py` triggers its
+  build-on-first-run. `examples/01-hello` pins the same binning and the same
+  two output shapes against three servers
 
 ## Client (`src/ui.jsx`)
 

From dd12576aa2f15509a90c0cd18c2227b00fd2d0e3 Mon Sep 17 00:00:00 2001
From: Barret Schloerke <barret@posit.co>
Date: Fri, 11 Sep 2026 17:34:31 -0400
Subject: [PATCH 3/3] test(examples): fix review findings in the in-memory
 example tests

- 07-plotly: hoist skip_if_not_installed("plotly") to file scope, since
  app.R calls plotly::renderPlotly() in server() and every testServer()
  call needs it, not just the scatter test
- 08-input-handler: replace a tautological stdlib assertion with an
  exact check on the echoed datetime; the handler decodes as UTC and
  strips tzinfo, so the repr is machine-independent. Fix the FEATURES.md
  leaf that claimed a tzinfo= in the repr.
---
 examples/07-plotly/tests/testthat/test-outputs.R | 13 ++++++++++---
 examples/08-input-handler/FEATURES.md            |  5 +++--
 examples/08-input-handler/tests/test_when.py     |  7 +++----
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/examples/07-plotly/tests/testthat/test-outputs.R b/examples/07-plotly/tests/testthat/test-outputs.R
index a1f198d2..924fc1b7 100644
--- a/examples/07-plotly/tests/testthat/test-outputs.R
+++ b/examples/07-plotly/tests/testthat/test-outputs.R
@@ -13,6 +13,10 @@
 # pkg-r/tests/testthat/test-examples.R.
 app_dir <- testthat::test_path("..", "..")
 
+# app.R calls plotly::renderPlotly() inside server(), so every testServer()
+# call here -- not just the scatter test -- needs plotly installed.
+testthat::skip_if_not_installed("plotly")
+
 test_that("greeting counts the points", {
   shiny::testServer(app_dir, {
     session$setInputs(num_points = 50)
@@ -33,8 +37,6 @@ test_that("greeting is NULL before the client's first message", {
 })
 
 test_that("scatter renders a plotly widget with no plotlyOutput() anywhere", {
-  skip_if_not_installed("plotly")
-
   shiny::testServer(app_dir, {
     session$setInputs(num_points = 50)
 
@@ -44,7 +46,12 @@ test_that("scatter renders a plotly widget with no plotlyOutput() anywhere", {
     # after the flush.
     expect_s3_class(output$scatter, "json")
     expect_match(output$scatter, '"type":"scatter"', fixed = TRUE)
-    dep_names <- vapply(attr(output$scatter, "deps"), `[[`, character(1), "name")
+    dep_names <- vapply(
+      attr(output$scatter, "deps"),
+      `[[`,
+      character(1),
+      "name"
+    )
     expect_true("plotly-main" %in% dep_names)
     # The *binding* JS is not in here: page_react() discovers it from the
     # render function and pushes it as a shinyreact-deps message instead,
diff --git a/examples/08-input-handler/FEATURES.md b/examples/08-input-handler/FEATURES.md
index ccab0e53..baaf3051 100644
--- a/examples/08-input-handler/FEATURES.md
+++ b/examples/08-input-handler/FEATURES.md
@@ -23,11 +23,12 @@ a unit test; `(verify)` marks a claim not yet checked against the code.
 ## Server (`app.py`, Express)
 
 - one output, `when_info` → `"<type name> → <repr>"`, e.g.
-  `"datetime → datetime.datetime(2026, 8, 28, 12, 0, tzinfo=...)"` `(test)`
+  `1756382400` → `"datetime → datetime.datetime(2025, 8, 28, 12, 0)"` `(test)`
+  - Shiny's handler decodes as UTC and strips the `tzinfo`, so the repr is
+    naive and machine-independent `(test)`
 - before the first client message, `input.when()` raises a silent exception, so
   `when_info` never renders — the `"—"` (em dash) branch in `app.py` is
   unreachable from a real client `(test)`
-- the example asserts nothing about the timezone the handler attaches
 - `[py]` only — this example has no R server; R's handler registry has no
   `shiny.datetime` equivalent, so the client is not portable as written
 
diff --git a/examples/08-input-handler/tests/test_when.py b/examples/08-input-handler/tests/test_when.py
index fafe63aa..c1adee84 100644
--- a/examples/08-input-handler/tests/test_when.py
+++ b/examples/08-input-handler/tests/test_when.py
@@ -11,7 +11,6 @@
 
 from __future__ import annotations
 
-import datetime
 from pathlib import Path
 
 from shiny.testserver import test_server
@@ -25,9 +24,9 @@ def test_the_handler_turns_unix_seconds_into_a_datetime() -> None:
         ts.set_inputs(**{"when:shiny.datetime": 1756382400})
         echoed = ts.get_output("when_info").value
 
-        assert echoed.startswith("datetime → datetime.datetime(")
-        # The example asserts nothing about the timezone, only the type.
-        assert datetime.datetime.fromtimestamp(1756382400).year == 2025
+        # Shiny's handler decodes as UTC and strips the tzinfo, so the value
+        # is the same on every machine: 1756382400 is 2025-08-28T12:00:00Z.
+        assert echoed == "datetime → datetime.datetime(2025, 8, 28, 12, 0)"
 
 
 def test_an_unsuffixed_value_is_not_coerced() -> None: