ansible-test - Replace pytest-forked (#80525)

- Unit tests now report warnings generated during test runs.
- Python 3.12 warnings about `os.fork` usage with threads (due to `pytest-xdist`) are suppressed.
- Added integration tests to verify forked test behavior.

4 files changed, 107 insertions, 2 deletions

diff --git a/test/lib/ansible_test/_data/requirements/units.txt b/test/lib/ansible_test/_data/requirements/units.txt
index d2f56d35a9..d723a65fc6 100644
--- a/test/lib/ansible_test/_data/requirements/units.txt
+++ b/test/lib/ansible_test/_data/requirements/units.txt
@@ -2,5 +2,4 @@ mock
 pytest
 pytest-mock
 pytest-xdist
-pytest-forked
 pyyaml  # required by the collection loader (only needed for collections)
diff --git a/test/lib/ansible_test/_internal/commands/units/__init__.py b/test/lib/ansible_test/_internal/commands/units/__init__.py
index 7d192e1be6..78dd849815 100644
--- a/test/lib/ansible_test/_internal/commands/units/__init__.py
+++ b/test/lib/ansible_test/_internal/commands/units/__init__.py
@@ -253,7 +253,6 @@ def command_units(args: UnitsConfig) -> None:
 
         cmd = [
             'pytest',
-            '--forked',
             '-r', 'a',
             '-n', str(args.num_workers) if args.num_workers else 'auto',
             '--color', 'yes' if args.color else 'no',
@@ -275,6 +274,8 @@ def command_units(args: UnitsConfig) -> None:
         if data_context().content.collection:
             plugins.append('ansible_pytest_collections')
 
+        plugins.append('ansible_forked')
+
         if plugins:
             env['PYTHONPATH'] += ':%s' % os.path.join(ANSIBLE_TEST_TARGET_ROOT, 'pytest/plugins')
             env['PYTEST_PLUGINS'] = ','.join(plugins)
diff --git a/test/lib/ansible_test/_util/controller/sanity/pylint/config/ansible-test-target.cfg b/test/lib/ansible_test/_util/controller/sanity/pylint/config/ansible-test-target.cfg
index e35301dd81..f8a0a8af3f 100644
--- a/test/lib/ansible_test/_util/controller/sanity/pylint/config/ansible-test-target.cfg
+++ b/test/lib/ansible_test/_util/controller/sanity/pylint/config/ansible-test-target.cfg
@@ -57,3 +57,5 @@ preferred-modules =
 # Listing them here makes it possible to enable the import-error check.
 ignored-modules =
     py,
+    pytest,
+    _pytest.runner,
diff --git a/test/lib/ansible_test/_util/target/pytest/plugins/ansible_forked.py b/test/lib/ansible_test/_util/target/pytest/plugins/ansible_forked.py
new file mode 100644
index 0000000000..d00d9e93d1
--- /dev/null
+++ b/test/lib/ansible_test/_util/target/pytest/plugins/ansible_forked.py
@@ -0,0 +1,103 @@
+"""Run each test in its own fork. PYTEST_DONT_REWRITE"""
+# MIT License (see licenses/MIT-license.txt or https://opensource.org/licenses/MIT)
+# Based on code originally from:
+# https://github.com/pytest-dev/pytest-forked
+# https://github.com/pytest-dev/py
+# TIP: Disable pytest-xdist when debugging internal errors in this plugin.
+from __future__ import absolute_import, division, print_function
+
+__metaclass__ = type
+
+import os
+import pickle
+import tempfile
+import warnings
+
+from pytest import Item, hookimpl
+
+try:
+    from pytest import TestReport
+except ImportError:
+    from _pytest.runner import TestReport  # Backwards compatibility with pytest < 7. Remove once Python 2.7 is not supported.
+
+from _pytest.runner import runtestprotocol
+
+
+@hookimpl(tryfirst=True)
+def pytest_runtest_protocol(item, nextitem):  # type: (Item, Item | None) -> object | None
+    """Entry point for enabling this plugin."""
+    # This is needed because pytest-xdist creates an OS thread (using execnet).
+    # See: https://github.com/pytest-dev/execnet/blob/d6aa1a56773c2e887515d63e50b1d08338cb78a7/execnet/gateway_base.py#L51
+    warnings.filterwarnings("ignore", "^This process .* is multi-threaded, use of .* may lead to deadlocks in the child.$", DeprecationWarning)
+
+    item_hook = item.ihook
+    item_hook.pytest_runtest_logstart(nodeid=item.nodeid, location=item.location)
+
+    reports = run_item(item, nextitem)
+
+    for report in reports:
+        item_hook.pytest_runtest_logreport(report=report)
+
+    item_hook.pytest_runtest_logfinish(nodeid=item.nodeid, location=item.location)
+
+    return True
+
+
+def run_item(item, nextitem):  # type: (Item, Item | None) -> list[TestReport]
+    """Run the item in a child process and return a list of reports."""
+    with tempfile.NamedTemporaryFile() as temp_file:
+        pid = os.fork()
+
+        if not pid:
+            temp_file.delete = False
+            run_child(item, nextitem, temp_file.name)
+
+        return run_parent(item, pid, temp_file.name)
+
+
+def run_child(item, nextitem, result_path):  # type: (Item, Item | None, str) -> None
+    """Run the item, record the result and exit. Called in the child process."""
+    with warnings.catch_warnings(record=True) as captured_warnings:
+        reports = runtestprotocol(item, nextitem=nextitem, log=False)
+
+    with open(result_path, "wb") as result_file:
+        pickle.dump((reports, captured_warnings), result_file)
+
+    os._exit(0)  # noqa
+
+
+def run_parent(item, pid, result_path):  # type: (Item, int, str) -> list[TestReport]
+    """Wait for the child process to exit and return the test reports. Called in the parent process."""
+    exit_code = waitstatus_to_exitcode(os.waitpid(pid, 0)[1])
+
+    if exit_code:
+        reason = "Test CRASHED with exit code {}.".format(exit_code)
+        report = TestReport(item.nodeid, item.location, {x: 1 for x in item.keywords}, "failed", reason, "call", user_properties=item.user_properties)
+
+        if item.get_closest_marker("xfail"):
+            report.outcome = "skipped"
+            report.wasxfail = reason
+
+        reports = [report]
+    else:
+        with open(result_path, "rb") as result_file:
+            reports, captured_warnings = pickle.load(result_file)  # type: list[TestReport], list[warnings.WarningMessage]
+
+        for warning in captured_warnings:
+            warnings.warn_explicit(warning.message, warning.category, warning.filename, warning.lineno)
+
+    return reports
+
+
+def waitstatus_to_exitcode(status):  # type: (int) -> int
+    """Convert a wait status to an exit code."""
+    # This function was added in Python 3.9.
+    # See: https://docs.python.org/3/library/os.html#os.waitstatus_to_exitcode
+
+    if os.WIFEXITED(status):
+        return os.WEXITSTATUS(status)
+
+    if os.WIFSIGNALED(status):
+        return -os.WTERMSIG(status)
+
+    raise ValueError(status)