Fixed #29127 -- Prevented DiscoverRunner from hiding tagged test with syntax errors.

This mades _FailedTest objects always match tags in DiscoverRunner.

django/test/runner.py

@@ -852,6 +852,10 @@ def partition_suite_by_case(suite):
 
 
 def test_match_tags(test, tags, exclude_tags):
+    if isinstance(test, unittest.loader._FailedTest):
+        # Tests that couldn't load always match to prevent tests from falsely
+        # passing due e.g. to syntax errors.
+        return True
     test_tags = set(getattr(test, 'tags', []))
     test_fn_name = getattr(test, '_testMethodName', str(test))
     if hasattr(test, test_fn_name):

docs/ref/django-admin.txt

@@ -1497,6 +1497,12 @@ don't.
 Runs only tests :ref:`marked with the specified tags <topics-tagging-tests>`.
 May be specified multiple times and combined with :option:`test --exclude-tag`.
 
+Tests that fail to load are always considered matching.
+
+.. versionchanged:: 4.0
+
+    In older versions, tests that failed to load did not match tags.
+
 .. option:: --exclude-tag EXCLUDE_TAGS
 
 Excludes tests :ref:`marked with the specified tags <topics-tagging-tests>`.

docs/releases/4.0.txt

@@ -373,6 +373,9 @@ Miscellaneous
   non-boolean attribute without a value equal to an attribute with the same
   name and value.
 
+* Tests that fail to load, for example due to syntax errors, now always match
+  when using :option:`test --tag`.
+
 .. _deprecated-features-4.0:
 
 Features deprecated in 4.0

tests/test_runner/test_discover_runner.py

@@ -2,6 +2,7 @@ import os
 import unittest.loader
 from argparse import ArgumentParser
 from contextlib import contextmanager
+from importlib import import_module
 from unittest import TestSuite, TextTestRunner, defaultTestLoader, mock
 
 from django.db import connections
@@ -259,6 +260,18 @@ class DiscoverRunnerTests(SimpleTestCase):
         self.assertEqual(count_tests(tags=['foo'], exclude_tags=['bar', 'baz']), 1)
         self.assertEqual(count_tests(exclude_tags=['foo']), 0)
 
+    def test_tag_fail_to_load(self):
+        with self.assertRaises(SyntaxError):
+            import_module('test_runner_apps.tagged.tests_syntax_error')
+        runner = DiscoverRunner(tags=['syntax_error'])
+        # A label that doesn't exist or cannot be loaded due to syntax errors
+        # is always considered matching.
+        suite = runner.build_suite(['doesnotexist', 'test_runner_apps.tagged'])
+        self.assertEqual([test.id() for test in suite], [
+            'unittest.loader._FailedTest.doesnotexist',
+            'unittest.loader._FailedTest.test_runner_apps.tagged.tests_syntax_error',
+        ])
+
     def test_included_tags_displayed(self):
         runner = DiscoverRunner(tags=['foo', 'bar'], verbosity=2)
         with captured_stdout() as stdout:

tests/test_runner_apps/tagged/tests_syntax_error.py

@@ -0,0 +1,11 @@
+from unittest import TestCase
+
+from django.test import tag
+
+
+@tag('syntax_error')
+class SyntaxErrorTestCase(TestCase):
+    pass
+
+
+1syntax_error  # NOQA