gh-109276: libregrtest calls random.seed() before each test

libregrtest now calls random.seed() before running each test file
when -r/--randomize command line option is used. Moreover, it's also
called in worker processes. It should help to make tests more
deterministic. Previously, it was only called once in the main
process before running all test files and it was not called in worker
processes.

* Convert some f-strings to regular strings in test_regrtest when
  f-string is not needed.
* Remove unused all_methods variable from test_regrtest.
* Add RunTests members are now mandatory.

Author: vstinner

Lib/test/libregrtest/main.py

@@ -112,8 +112,11 @@ def __init__(self, ns: Namespace):
         self.junit_filename: StrPath | None = ns.xmlpath
         self.memory_limit: str | None = ns.memlimit
         self.gc_threshold: int | None = ns.threshold
-        self.use_resources: list[str] = ns.use_resources
-        self.python_cmd: list[str] | None = ns.python
+        self.use_resources: tuple[str] = tuple(ns.use_resources)
+        if ns.python:
+            self.python_cmd: tuple[str] = tuple(ns.python)
+        else:
+            self.python_cmd = None
         self.coverage: bool = ns.trace
         self.coverage_dir: StrPath | None = ns.coverdir
         self.tmp_dir: StrPath | None = ns.tempdir
@@ -377,8 +380,11 @@ def create_run_tests(self, tests: TestTuple):
         return RunTests(
             tests,
             fail_fast=self.fail_fast,
+            fail_env_changed=self.fail_env_changed,
             match_tests=self.match_tests,
             ignore_tests=self.ignore_tests,
+            match_tests_dict=None,
+            rerun=None,
             forever=self.forever,
             pgo=self.pgo,
             pgo_extended=self.pgo_extended,
@@ -393,6 +399,8 @@ def create_run_tests(self, tests: TestTuple):
             gc_threshold=self.gc_threshold,
             use_resources=self.use_resources,
             python_cmd=self.python_cmd,
+            randomize=self.randomize,
+            random_seed=self.random_seed,
         )
 
     def _run_tests(self, selected: TestTuple, tests: TestList | None) -> int:

Lib/test/libregrtest/runtests.py

@@ -16,26 +16,28 @@ class HuntRefleak:
 @dataclasses.dataclass(slots=True, frozen=True)
 class RunTests:
     tests: TestTuple
-    fail_fast: bool = False
-    fail_env_changed: bool = False
-    match_tests: FilterTuple | None = None
-    ignore_tests: FilterTuple | None = None
-    match_tests_dict: FilterDict | None = None
-    rerun: bool = False
-    forever: bool = False
-    pgo: bool = False
-    pgo_extended: bool = False
-    output_on_failure: bool = False
-    timeout: float | None = None
-    verbose: int = 0
-    quiet: bool = False
-    hunt_refleak: HuntRefleak | None = None
-    test_dir: StrPath | None = None
-    use_junit: bool = False
-    memory_limit: str | None = None
-    gc_threshold: int | None = None
-    use_resources: list[str] = dataclasses.field(default_factory=list)
-    python_cmd: list[str] | None = None
+    fail_fast: bool
+    fail_env_changed: bool
+    match_tests: FilterTuple | None
+    ignore_tests: FilterTuple | None
+    match_tests_dict: FilterDict | None
+    rerun: bool
+    forever: bool
+    pgo: bool
+    pgo_extended: bool
+    output_on_failure: bool
+    timeout: float | None
+    verbose: int
+    quiet: bool
+    hunt_refleak: HuntRefleak | None
+    test_dir: StrPath | None
+    use_junit: bool
+    memory_limit: str | None
+    gc_threshold: int | None
+    use_resources: tuple[str]
+    python_cmd: tuple[str] | None
+    randomize: bool
+    random_seed: int | None
 
     def copy(self, **override):
         state = dataclasses.asdict(self)

Lib/test/libregrtest/setup.py

@@ -1,5 +1,6 @@
 import faulthandler
 import os
+import random
 import signal
 import sys
 import unittest
@@ -127,3 +128,6 @@ def setup_tests(runtests: RunTests):
 
     if runtests.gc_threshold is not None:
         gc.set_threshold(runtests.gc_threshold)
+
+    if runtests.randomize:
+        random.seed(runtests.random_seed)

Lib/test/test_regrtest.py

@@ -11,6 +11,7 @@
 import locale
 import os.path
 import platform
+import random
 import re
 import subprocess
 import sys
@@ -504,7 +505,7 @@ def list_regex(line_format, tests):
         if rerun is not None:
             regex = list_regex('%s re-run test%s', [rerun.name])
             self.check_line(output, regex)
-            regex = LOG_PREFIX + fr"Re-running 1 failed tests in verbose mode"
+            regex = LOG_PREFIX + r"Re-running 1 failed tests in verbose mode"
             self.check_line(output, regex)
             regex = fr"Re-running {rerun.name} in verbose mode"
             if rerun.match:
@@ -1018,13 +1019,13 @@ def test_run(self):
                                   stats=TestStats(4, 1),
                                   forever=True)
 
-    def check_leak(self, code, what, *, multiprocessing=False):
+    def check_leak(self, code, what, *, run_workers=False):
         test = self.create_test('huntrleaks', code=code)
 
         filename = 'reflog.txt'
         self.addCleanup(os_helper.unlink, filename)
         cmd = ['--huntrleaks', '6:3:']
-        if multiprocessing:
+        if run_workers:
             cmd.append('-j1')
         cmd.append(test)
         output = self.run_tests(*cmd,
@@ -1043,7 +1044,7 @@ def check_leak(self, code, what, *, multiprocessing=False):
             self.assertIn(line2, reflog)
 
     @unittest.skipUnless(support.Py_DEBUG, 'need a debug build')
-    def check_huntrleaks(self, *, multiprocessing: bool):
+    def check_huntrleaks(self, *, run_workers: bool):
         # test --huntrleaks
         code = textwrap.dedent("""
             import unittest
@@ -1054,13 +1055,13 @@ class RefLeakTest(unittest.TestCase):
                 def test_leak(self):
                     GLOBAL_LIST.append(object())
         """)
-        self.check_leak(code, 'references', multiprocessing=multiprocessing)
+        self.check_leak(code, 'references', run_workers=run_workers)
 
     def test_huntrleaks(self):
-        self.check_huntrleaks(multiprocessing=False)
+        self.check_huntrleaks(run_workers=False)
 
     def test_huntrleaks_mp(self):
-        self.check_huntrleaks(multiprocessing=True)
+        self.check_huntrleaks(run_workers=True)
 
     @unittest.skipUnless(support.Py_DEBUG, 'need a debug build')
     def test_huntrleaks_fd_leak(self):
@@ -1138,8 +1139,6 @@ def test_method3(self):
                 def test_method4(self):
                     pass
         """)
-        all_methods = ['test_method1', 'test_method2',
-                       'test_method3', 'test_method4']
         testname = self.create_test(code=code)
 
         # only run a subset
@@ -1761,7 +1760,7 @@ def test_mp_decode_error(self):
             if encoding is None:
                 encoding = sys.__stdout__.encoding
                 if encoding is None:
-                    self.skipTest(f"cannot get regrtest worker encoding")
+                    self.skipTest("cannot get regrtest worker encoding")
 
         nonascii = b"byte:\xa0\xa9\xff\n"
         try:
@@ -1788,7 +1787,7 @@ def test_mp_decode_error(self):
                                   stats=0)
 
     def test_doctest(self):
-        code = textwrap.dedent(fr'''
+        code = textwrap.dedent(r'''
             import doctest
             import sys
             from test import support
@@ -1826,6 +1825,46 @@ def load_tests(loader, tests, pattern):
                                   randomize=True,
                                   stats=TestStats(1, 1, 0))
 
+    def _check_random_seed(self, run_workers: bool):
+        # gh-109276: When -r/--randomize is used, random.seed() is called
+        # with the same random seed before running each test file.
+        code = textwrap.dedent(r'''
+            import random
+            import unittest
+
+            class RandomSeedTest(unittest.TestCase):
+                def test_randint(self):
+                    numbers = [random.randint(0, 1000) for _ in range(10)]
+                    print(f"Random numbers: {numbers}")
+        ''')
+        tests = [self.create_test(name=f'test_random{i}', code=code)
+                 for i in range(1, 3+1)]
+
+        random_seed = 856_656_202
+        cmd = ["--randomize", f"--randseed={random_seed}"]
+        if run_workers:
+            # run as many worker processes than the number of tests
+            cmd.append(f'-j{len(tests)}')
+        cmd.extend(tests)
+        output = self.run_tests(*cmd)
+
+        random.seed(random_seed)
+        # make the assumption that nothing consume entry between libregrest
+        # setup_tests() calls random.seed() and RandomSeedTest calling
+        # random.randint().
+        numbers = [random.randint(0, 1000) for _ in range(10)]
+        expected = f"Random numbers: {numbers}"
+
+        regex = r'^Random numbers: .*$'
+        matches = re.findall(regex, output, flags=re.MULTILINE)
+        self.assertEqual(matches, [expected] * len(tests))
+
+    def test_random_seed(self):
+        self._check_random_seed(run_workers=False)
+
+    def test_random_seed_workers(self):
+        self._check_random_seed(run_workers=True)
+
 
 class TestUtils(unittest.TestCase):
     def test_format_duration(self):

Misc/NEWS.d/next/Tests/2023-09-11-19-11-57.gh-issue-109276.qxI4OG.rst

@@ -0,0 +1,6 @@
+libregrtest now calls :func:`random.seed()` before running each test file
+when ``-r/--randomize`` command line option is used. Moreover, it's also
+called in worker processes.  It should help to make tests more
+deterministic. Previously, it was only called once in the main process before
+running all test files and it was not called in worker processes.  Patch by
+Victor Stinner.