Fixed #27430 -- Added -b/--buffer option to DiscoverRunner.

django/test/runner.py

@@ -434,7 +434,7 @@ class DiscoverRunner:
                  interactive=True, failfast=False, keepdb=False,
                  reverse=False, debug_mode=False, debug_sql=False, parallel=0,
                  tags=None, exclude_tags=None, test_name_patterns=None,
-                 pdb=False, **kwargs):
+                 pdb=False, buffer=False, **kwargs):
 
         self.pattern = pattern
         self.top_level = top_level
@@ -451,6 +451,12 @@ class DiscoverRunner:
         self.pdb = pdb
         if self.pdb and self.parallel > 1:
             raise ValueError('You cannot use --pdb with parallel tests; pass --parallel=1 to use it.')
+        self.buffer = buffer
+        if self.buffer and self.parallel > 1:
+            raise ValueError(
+                'You cannot use -b/--buffer with parallel tests; pass '
+                '--parallel=1 to use it.'
+            )
         self.test_name_patterns = None
         if test_name_patterns:
             # unittest does not export the _convert_select_pattern function
@@ -503,6 +509,10 @@ class DiscoverRunner:
             '--pdb', action='store_true',
             help='Runs a debugger (pdb, or ipdb if installed) on error or failure.'
         )
+        parser.add_argument(
+            '-b', '--buffer', action='store_true',
+            help='Discard output from passing tests.',
+        )
         if PY37:
             parser.add_argument(
                 '-k', action='append', dest='test_name_patterns',
@@ -617,6 +627,7 @@ class DiscoverRunner:
             'failfast': self.failfast,
             'resultclass': self.get_resultclass(),
             'verbosity': self.verbosity,
+            'buffer': self.buffer,
         }
 
     def run_checks(self):

docs/ref/django-admin.txt

@@ -1462,6 +1462,13 @@ Runs test methods and classes matching test name patterns, in the same way as
 Spawns a ``pdb`` debugger at each test error or failure. If you have it
 installed, ``ipdb`` is used instead.
 
+.. django-admin-option:: --buffer, -b
+
+.. versionadded:: 3.1
+
+Discards output (``stdout`` and ``stderr``) for passing tests, in the same way
+as :option:`unittest's --buffer option<unittest.-b>`.
+
 ``testserver``
 --------------
 

docs/releases/3.1.txt

@@ -257,6 +257,9 @@ Tests
 * The new :setting:`MIGRATE <TEST_MIGRATE>` test database setting allows
   disabling of migrations during a test database creation.
 
+* Django test runner now supports a :option:`test --buffer` option to discard
+  output for passing tests.
+
 URLs
 ~~~~
 

tests/runtests.py

@@ -281,7 +281,7 @@ class ActionSelenium(argparse.Action):
 
 def django_tests(verbosity, interactive, failfast, keepdb, reverse,
                  test_labels, debug_sql, parallel, tags, exclude_tags,
-                 test_name_patterns, start_at, start_after, pdb):
+                 test_name_patterns, start_at, start_after, pdb, buffer):
     state = setup(verbosity, test_labels, parallel, start_at, start_after)
     extra_tests = []
 
@@ -302,6 +302,7 @@ def django_tests(verbosity, interactive, failfast, keepdb, reverse,
         exclude_tags=exclude_tags,
         test_name_patterns=test_name_patterns,
         pdb=pdb,
+        buffer=buffer,
     )
     failures = test_runner.run_tests(
         test_labels or get_installed(),
@@ -497,6 +498,10 @@ if __name__ == "__main__":
         '--pdb', action='store_true',
         help='Runs the PDB debugger on error or failure.'
     )
+    parser.add_argument(
+        '-b', '--buffer', action='store_true',
+        help='Discard output of passing tests.',
+    )
     if PY37:
         parser.add_argument(
             '-k', dest='test_name_patterns', action='append',
@@ -563,7 +568,7 @@ if __name__ == "__main__":
             options.debug_sql, options.parallel, options.tags,
             options.exclude_tags,
             getattr(options, 'test_name_patterns', None),
-            options.start_at, options.start_after, options.pdb,
+            options.start_at, options.start_after, options.pdb, options.buffer,
         )
         if failures:
             sys.exit(1)

tests/test_runner/test_discover_runner.py

@@ -6,7 +6,7 @@ from unittest import TestSuite, TextTestRunner, defaultTestLoader, skipUnless
 from django.db import connections
 from django.test import SimpleTestCase
 from django.test.runner import DiscoverRunner
-from django.test.utils import captured_stdout
+from django.test.utils import captured_stderr, captured_stdout
 from django.utils.version import PY37
 
 
@@ -269,6 +269,34 @@ class DiscoverRunnerTests(SimpleTestCase):
         with self.assertRaisesMessage(ValueError, msg):
             DiscoverRunner(pdb=True, parallel=2)
 
+    def test_buffer_with_parallel(self):
+        msg = (
+            'You cannot use -b/--buffer with parallel tests; pass '
+            '--parallel=1 to use it.'
+        )
+        with self.assertRaisesMessage(ValueError, msg):
+            DiscoverRunner(buffer=True, parallel=2)
+
+    def test_buffer_mode_test_pass(self):
+        runner = DiscoverRunner(buffer=True, verbose=0)
+        with captured_stdout() as stdout, captured_stderr() as stderr:
+            suite = runner.build_suite([
+                'test_runner_apps.buffer.tests_buffer.WriteToStdoutStderrTestCase.test_pass',
+            ])
+            runner.run_suite(suite)
+        self.assertNotIn('Write to stderr.', stderr.getvalue())
+        self.assertNotIn('Write to stdout.', stdout.getvalue())
+
+    def test_buffer_mode_test_fail(self):
+        runner = DiscoverRunner(buffer=True, verbose=0)
+        with captured_stdout() as stdout, captured_stderr() as stderr:
+            suite = runner.build_suite([
+                'test_runner_apps.buffer.tests_buffer.WriteToStdoutStderrTestCase.test_fail',
+            ])
+            runner.run_suite(suite)
+        self.assertIn('Write to stderr.', stderr.getvalue())
+        self.assertIn('Write to stdout.', stdout.getvalue())
+
 
 class DiscoverRunnerGetDatabasesTests(SimpleTestCase):
     runner = DiscoverRunner(verbosity=2)

tests/test_runner_apps/buffer/tests_buffer.py

@@ -0,0 +1,14 @@
+import sys
+from unittest import TestCase
+
+
+class WriteToStdoutStderrTestCase(TestCase):
+    def test_pass(self):
+        sys.stderr.write('Write to stderr.')
+        sys.stdout.write('Write to stdout.')
+        self.assertTrue(True)
+
+    def test_fail(self):
+        sys.stderr.write('Write to stderr.')
+        sys.stdout.write('Write to stdout.')
+        self.assertTrue(False)