Patch random module during unpickling to ensure deterministic seeding in subprocesses

Author: LuKrO2011

src/pynguin/generator.py

@@ -261,6 +261,10 @@ def _patch_random() -> None:
         def _deterministic_random_seed(self: random.Random, x=None) -> None:
             if x is None:
                 x = config.configuration.seeding.seed
+            elif type(x).__hash__ is object.__hash__:
+                # If x is an object that uses the default id-based hash, we replace it with
+                # a deterministic string to avoid non-determinism from memory addresses.
+                x = f"{type(x).__module__}.{type(x).__name__}"
             orig_random_seed(self, x)
             tracked.add(self)
 

src/pynguin/testcase/execution.py

@@ -1267,6 +1267,27 @@ def _after_statement_execution(
     SUPPORTED_EXIT_CODE_MESSAGES[-signal.SIGSEGV] = "Segmentation fault detected"
 
 
+class PatchRandomOnUnpickle:
+    """A hook that patches random when unpickled in a subprocess.
+
+    This ensures that random.Random.seed is patched before the SUT is unpickled
+    and potentially creates new random.Random instances (e.g., mimesis).
+    """
+
+    def __init__(self):
+        """Create a new hook."""
+        self._config = config.configuration
+
+    def __getstate__(self):
+        return {"config": self._config}
+
+    def __setstate__(self, state):
+        config.configuration = state["config"]
+        from pynguin.generator import _patch_random  # noqa: PLC0415
+
+        _patch_random()
+
+
 class SubprocessTestCaseExecutor(TestCaseExecutor):
     """An executor that executes the generated test cases in a subprocess."""
 
@@ -1472,6 +1493,7 @@ def _setup_subprocess_execution(
         remote_observers = tuple(self._yield_remote_observers())
 
         args = (
+            PatchRandomOnUnpickle(),
             self._subject_properties,
             self._module_provider,
             self._maximum_test_execution_timeout,
@@ -1723,6 +1745,7 @@ def _fix_assertion_trace(
 
     @staticmethod
     def _execute_test_cases_in_subprocess(  # noqa: PLR0917
+        _patch_random_hook: object,
         subject_properties: SubjectProperties,
         module_provider: ModuleProvider,
         maximum_test_execution_timeout: int,

src/pynguin/testcase/export.py

@@ -296,6 +296,8 @@ def __create_patch_nodes(seed: int) -> list[ast.stmt]:
             "    def _pynguin_deterministic_seed(self, x=None):\n"
             "        if x is None:\n"
             f"            x = {seed}\n"
+            "        elif type(x).__hash__ is object.__hash__:\n"
+            "            x = f'{type(x).__module__}.{type(x).__name__}'\n"
             "        _pynguin_orig_seed(self, x)\n"
             "        _pynguin_tracked.add(self)\n"
             "    _pynguin_deterministic_seed.__pynguin_patched__ = True\n"
@@ -477,6 +479,7 @@ def save_module_to_file(
         output = output.replace(
             "random.Random.seed = _pynguin_deterministic_seed",
             "random.Random.seed = _pynguin_deterministic_seed\n",
+            1,
         )
 
         if module_name_with_coverage:

tests/testcase/execution/test_subprocesstestcaseexecutor.py

@@ -25,7 +25,11 @@
 from pynguin.analyses.typesystem import InferredSignature, NoneType
 from pynguin.instrumentation.machinery import install_import_hook
 from pynguin.instrumentation.tracer import SubjectProperties
-from pynguin.testcase.execution import ModuleProvider, SubprocessTestCaseExecutor
+from pynguin.testcase.execution import (
+    ModuleProvider,
+    PatchRandomOnUnpickle,
+    SubprocessTestCaseExecutor,
+)
 from pynguin.utils.generic.genericaccessibleobject import GenericFunction
 from tests.fixtures.crash.seg_fault import cause_segmentation_fault
 
@@ -90,6 +94,7 @@ def test_subprocess_exception_suppression(subject_properties: SubjectProperties)
         # This should not raise an exception because the exception should be caught
         # and suppressed inside the method
         SubprocessTestCaseExecutor._execute_test_cases_in_subprocess(
+            PatchRandomOnUnpickle(),
             subject_properties,
             module_provider,
             maximum_test_execution_timeout,
@@ -141,6 +146,7 @@ def test_subprocess_exception_logging(caplog, subject_properties: SubjectPropert
 
         # Call the method directly
         SubprocessTestCaseExecutor._execute_test_cases_in_subprocess(
+            PatchRandomOnUnpickle(),
             subject_properties,
             module_provider,
             maximum_test_execution_timeout,