diff --git a/utest/test_js_extension_call.py b/utest/test_js_extension_call.py
index 214854e05..4fe16bf57 100644
--- a/utest/test_js_extension_call.py
+++ b/utest/test_js_extension_call.py
@@ -1,9 +1,12 @@
 import inspect
 import json
+import math
 from contextlib import contextmanager
 from datetime import timedelta
 from types import SimpleNamespace
 
+import pytest
+
 from Browser import Browser
 from Browser.base import LibraryComponent
 from Browser.utils.data_types import Scope
@@ -12,6 +15,7 @@
 class RecordingPlaywright:
     def __init__(self):
         self.requests = []
+        self.responses = []
 
     @contextmanager
     def grpc_channel(self):
@@ -19,7 +23,7 @@ def grpc_channel(self):
 
     def CallExtensionKeyword(self, request):  # noqa: N802 - the name of the gRPC method
         self.requests.append(request)
-        return []
+        return self.responses
 
     def SetTimeout(self, request):  # noqa: N802 - the name of the gRPC method
         return SimpleNamespace(log="")
@@ -28,13 +32,21 @@ def payload(self) -> dict:
         return json.loads(self.requests[-1].arguments)
 
 
-def library_with_recorded_calls(
-    tmpdir, monkeypatch
-) -> tuple[Browser, RecordingPlaywright]:
+@pytest.fixture
+def playwright() -> RecordingPlaywright:
+    return RecordingPlaywright()
+
+
+@pytest.fixture
+def library(tmpdir, monkeypatch, playwright: RecordingPlaywright) -> Browser:
     monkeypatch.setattr(Browser, "_output_dir", tmpdir)
     library = Browser(timeout=timedelta(seconds=7))
-    library._playwright = RecordingPlaywright()
-    return library, library._playwright
+    library._playwright = playwright
+    return library
+
+
+def extension_response(log: str, body_part: str = "") -> SimpleNamespace:
+    return SimpleNamespace(log=log, bodyPart=body_part, json="")
 
 
 def generated_keyword(library: Browser, name: str, arguments: str):
@@ -44,9 +56,8 @@ def generated_keyword(library: Browser, name: str, arguments: str):
 
 
 def test_generated_keyword_passes_the_library_timeout_as_default_timeout(
-    tmpdir, monkeypatch
+    library: Browser, playwright: RecordingPlaywright
 ):
-    library, playwright = library_with_recorded_calls(tmpdir, monkeypatch)
     keyword = generated_keyword(library, "openOwnContext", "url, defaultTimeout")
 
     keyword("https://a.b")
@@ -57,8 +68,9 @@ def test_generated_keyword_passes_the_library_timeout_as_default_timeout(
     }
 
 
-def test_generated_keyword_reads_the_library_timeout_at_each_call(tmpdir, monkeypatch):
-    library, playwright = library_with_recorded_calls(tmpdir, monkeypatch)
+def test_generated_keyword_reads_the_library_timeout_at_each_call(
+    library: Browser, playwright: RecordingPlaywright
+):
     keyword = generated_keyword(library, "openOwnContext", "defaultTimeout")
 
     library.set_browser_timeout(timedelta(seconds=3), Scope.Global)
@@ -67,9 +79,9 @@ def test_generated_keyword_reads_the_library_timeout_at_each_call(tmpdir, monkey
     assert playwright.payload() == {"arguments": [["defaultTimeout", 3000]]}
 
 
-def test_other_generated_keywords_send_only_their_arguments(tmpdir, monkeypatch):
-    library, playwright = library_with_recorded_calls(tmpdir, monkeypatch)
-
+def test_other_generated_keywords_send_only_their_arguments(
+    library: Browser, playwright: RecordingPlaywright
+):
     generated_keyword(library, "clickTwice", "selector, page")("#button")
 
     assert playwright.payload() == {
@@ -77,11 +89,86 @@ def test_other_generated_keywords_send_only_their_arguments(tmpdir, monkeypatch)
     }
 
 
-def test_call_js_keyword_sends_the_arguments_as_given(tmpdir, monkeypatch):
-    library, playwright = library_with_recorded_calls(tmpdir, monkeypatch)
-
+def test_call_js_keyword_sends_the_arguments_as_given(
+    library: Browser, playwright: RecordingPlaywright
+):
     library.call_js_keyword("openOwnContext", url="https://a.b", defaultTimeout=5000)
 
     assert playwright.payload() == {
         "arguments": [["url", "https://a.b"], ["defaultTimeout", 5000]]
     }
+
+
+def test_generated_keyword_joins_the_body_parts_of_a_chunked_result(
+    library: Browser, playwright: RecordingPlaywright
+):
+    playwright.responses = [
+        extension_response("ok chunk 0", '{"name": "J'),
+        extension_response("ok", 'örn", "size": 2}'),
+    ]
+
+    result = generated_keyword(library, "describe", "")()
+
+    assert result == {"name": "Jörn", "size": 2}
+
+
+def test_generated_keyword_returns_none_when_the_function_returns_nothing(
+    library: Browser, playwright: RecordingPlaywright
+):
+    playwright.responses = [extension_response("ok")]
+
+    assert generated_keyword(library, "closeAll", "")() is None
+
+
+def test_generated_keyword_sends_its_varargs_as_one_args_list(
+    library: Browser, playwright: RecordingPlaywright
+):
+    keyword = generated_keyword(library, "typeAll", "selector, args, logger")
+
+    keyword("#field", "first", "second")
+
+    assert playwright.payload() == {
+        "arguments": [
+            ["selector", "#field"],
+            ["args", ["first", "second"]],
+            ["logger", "RESERVED"],
+        ]
+    }
+
+
+def test_generated_keyword_takes_its_defaults_from_the_javascript_signature(
+    library: Browser,
+):
+    keyword = generated_keyword(
+        library,
+        "measure",
+        'label = "width", count = 3, ratio = NaN, upper = Infinity, '
+        "lower = -Infinity, strict = false, limit = null, unit = undefined",
+    )
+
+    defaults = {
+        name: parameter.default
+        for name, parameter in inspect.signature(keyword).parameters.items()
+    }
+
+    assert math.isnan(defaults.pop("ratio"))
+    assert defaults == {
+        "label": "width",
+        "count": 3,
+        "upper": math.inf,
+        "lower": -math.inf,
+        "strict": False,
+        "limit": None,
+        "unit": None,
+    }
+
+
+def test_generated_keyword_sends_a_test_scoped_timeout(
+    library: Browser, playwright: RecordingPlaywright
+):
+    keyword = generated_keyword(library, "openOwnContext", "defaultTimeout")
+
+    library.set_browser_timeout(timedelta(milliseconds=1500), Scope.Test)
+    keyword()
+
+    assert playwright.payload() == {"arguments": [["defaultTimeout", 1500]]}