Skip the module-release test once core stops leaking; fix a comment

policyengine_uk/tests/conftest.py

@@ -36,10 +36,10 @@ def pytest_collection_modifyitems(config, items):
 # a module named "<id(system)>_<path hash>_<file name>" and registers it in
 # sys.modules, where it stays after the system is garbage collected. Every
 # Simulation builds its own system, so each one leaves about 1,000 modules
-# (roughly 10 MB) behind, and the property tests build hundreds: one test
-# process grew to 15.7 GB on a 16 GB CI runner. After each test, drop the
-# modules of systems that no longer exist; live systems keep theirs. Remove
-# this once policyengine-core stops leaking them
+# (roughly 10 MB) behind, and the property tests build hundreds: running the
+# suite serially used 99% of a 16 GB CI runner's memory. After each test, drop
+# the modules of systems that no longer exist; live systems keep theirs.
+# Remove this once policyengine-core stops leaking them
 # (PolicyEngine/policyengine-core#520).
 _VARIABLE_MODULE_NAME = re.compile(r"(\d+)_-?\d+_")
 
@@ -66,8 +66,8 @@ def release_dead_variable_modules(max_owners: int = 8) -> int:
     for owner, names in owners.items():
         if owner not in live:
             for name in names:
-                sys.modules.pop(name, None)
-            released += len(names)
+                if sys.modules.pop(name, None) is not None:
+                    released += 1
     return released
 
 

policyengine_uk/tests/test_variable_module_release.py

@@ -4,14 +4,18 @@
 under the system's id and never removes them. The conftest's
 ``release_dead_variable_modules`` drops those of systems that no longer exist,
 which keeps a long test process's memory flat. If core stops leaking the
-modules (PolicyEngine/policyengine-core#520), the precondition below fails
-and the workaround can go.
+modules (PolicyEngine/policyengine-core#520), the first test skips with a
+note to remove the workaround, rather than failing every PR after a core
+upgrade. If core keeps leaking but names the modules differently, it fails,
+because the release would then silently do nothing.
 """
 
 import gc
 import sys
 from pathlib import Path
 
+import pytest
+
 from policyengine_uk import Simulation
 
 SITUATION = {
@@ -41,10 +45,18 @@ def test_dead_systems_modules_are_released_and_live_ones_kept(request):
     dropped_owner = str(id(dropped.tax_benefit_system))
     expected = dropped.calculate("income_tax", 2026)
 
-    assert _modules_of(dropped_owner), (
-        "policyengine-core no longer registers variable modules under the "
-        "system's id; the conftest workaround may no longer be needed"
-    )
+    # The module core loaded the income_tax variable from, for this system.
+    module = type(dropped.tax_benefit_system.variables["income_tax"]).__module__
+    if module not in sys.modules:
+        pytest.skip(
+            "policyengine-core no longer keeps variable modules in sys.modules "
+            "(policyengine-core#520 fixed?); remove "
+            "release_dead_variable_modules from conftest.py and this test"
+        )
+    # Core still keeps them, so the conftest pattern must still recognise them,
+    # or the release would silently do nothing.
+    assert module.startswith(dropped_owner + "_"), module
+    assert _conftest(request)._VARIABLE_MODULE_NAME.match(module), module
     del dropped
     gc.collect()