Fixed #32808 -- Prevented DiscoverRunner.build_suite() from mutating test loader patterns.

Thanks Chris Jerdonek for the report and reviews.

1 files changed, 32 insertions, 0 deletions

diff --git a/tests/test_runner/test_discover_runner.py b/tests/test_runner/test_discover_runner.py
index 692575b028..4eff76c5fd 100644
--- a/tests/test_runner/test_discover_runner.py
+++ b/tests/test_runner/test_discover_runner.py
@@ -26,6 +26,16 @@ def change_cwd(directory):
         os.chdir(old_cwd)
 
 
+@contextmanager
+def change_loader_patterns(patterns):
+    original_patterns = DiscoverRunner.test_loader.testNamePatterns
+    DiscoverRunner.test_loader.testNamePatterns = patterns
+    try:
+        yield
+    finally:
+        DiscoverRunner.test_loader.testNamePatterns = original_patterns
+
+
 class DiscoverRunnerTests(SimpleTestCase):
 
     @staticmethod
@@ -122,6 +132,28 @@ class DiscoverRunnerTests(SimpleTestCase):
                 ).build_suite(['test_runner_apps.simple'])
                 self.assertEqual(expected, self.get_test_methods_names(suite))
 
+    def test_loader_patterns_not_mutated(self):
+        runner = DiscoverRunner(test_name_patterns=['test_sample'], verbosity=0)
+        tests = [
+            ('test_runner_apps.sample.tests', 1),
+            ('test_runner_apps.sample.tests.Test.test_sample', 1),
+            ('test_runner_apps.sample.empty', 0),
+            ('test_runner_apps.sample.tests_sample.EmptyTestCase', 0),
+        ]
+        for test_labels, tests_count in tests:
+            with self.subTest(test_labels=test_labels):
+                with change_loader_patterns(['UnittestCase1']):
+                    count = runner.build_suite([test_labels]).countTestCases()
+                    self.assertEqual(count, tests_count)
+                    self.assertEqual(runner.test_loader.testNamePatterns, ['UnittestCase1'])
+
+    def test_loader_patterns_not_mutated_when_test_label_is_file_path(self):
+        runner = DiscoverRunner(test_name_patterns=['test_sample'], verbosity=0)
+        with change_cwd('.'), change_loader_patterns(['UnittestCase1']):
+            with self.assertRaises(RuntimeError):
+                runner.build_suite(['test_discover_runner.py'])
+            self.assertEqual(runner.test_loader.testNamePatterns, ['UnittestCase1'])
+
     def test_file_path(self):
         with change_cwd(".."):
             count = DiscoverRunner(verbosity=0).build_suite(