Fixed #31621 -- Added support for '--parallel auto' to test management command.

django/test/runner.py

@@ -1,3 +1,4 @@
+import argparse
 import ctypes
 import faulthandler
 import hashlib
@@ -335,16 +336,20 @@ class RemoteTestRunner:
         return result
 
 
-def default_test_processes():
-    """Default number of test processes when using the --parallel option."""
+def parallel_type(value):
+    """Parse value passed to the --parallel option."""
     # The current implementation of the parallel test runner requires
     # multiprocessing to start subprocesses with fork().
     if multiprocessing.get_start_method() != 'fork':
         return 1
-    try:
-        return int(os.environ['DJANGO_TEST_PROCESSES'])
-    except KeyError:
+    if value == 'auto':
         return multiprocessing.cpu_count()
+    try:
+        return int(value)
+    except ValueError:
+        raise argparse.ArgumentTypeError(
+            f"{value!r} is not an integer or the string 'auto'"
+        )
 
 
 _worker_id = 0
@@ -611,10 +616,17 @@ class DiscoverRunner:
             '-d', '--debug-sql', action='store_true',
             help='Prints logged SQL queries on failure.',
         )
+        try:
+            default_parallel = int(os.environ['DJANGO_TEST_PROCESSES'])
+        except KeyError:
+            default_parallel = 0
         parser.add_argument(
-            '--parallel', nargs='?', default=1, type=int,
-            const=default_test_processes(), metavar='N',
-            help='Run tests using up to N parallel processes.',
+            '--parallel', nargs='?', const='auto', default=default_parallel,
+            type=parallel_type, metavar='N',
+            help=(
+                'Run tests using up to N parallel processes. Use the value '
+                '"auto" to run one test process for each processor core.'
+            ),
         )
         parser.add_argument(
             '--tag', action='append', dest='tags',

docs/ref/django-admin.txt

@@ -1467,10 +1467,12 @@ Enables :ref:`SQL logging <django-db-logger>` for failing tests. If
 Runs tests in separate parallel processes. Since modern processors have
 multiple cores, this allows running tests significantly faster.
 
-By default ``--parallel`` runs one process per core according to
-:func:`multiprocessing.cpu_count()`. You can adjust the number of processes
-either by providing it as the option's value, e.g. ``--parallel=4``, or by
-setting the :envvar:`DJANGO_TEST_PROCESSES` environment variable.
+Using ``--parallel`` without a value, or with the value ``auto``, runs one test
+process per core according to :func:`multiprocessing.cpu_count()`. You can
+override this by passing the desired number of processes, e.g.
+``--parallel 4``. You can also enable ``--parallel`` without passing the flag
+by setting the :envvar:`DJANGO_TEST_PROCESSES` environment variable to the
+desired number of processes.
 
 Django distributes test cases — :class:`unittest.TestCase` subclasses — to
 subprocesses. If there are fewer test cases than configured processes, Django
@@ -1511,6 +1513,10 @@ don't.
     in order to exchange them between processes. See
     :ref:`python:pickle-picklable` for details.
 
+.. versionchanged:: 4.0
+
+    Support for the value ``auto`` was added.
+
 .. option:: --tag TAGS
 
 Runs only tests :ref:`marked with the specified tags <topics-tagging-tests>`.

docs/releases/4.0.txt

@@ -350,6 +350,9 @@ Tests
 * Django test runner now supports a :option:`--shuffle <test --shuffle>` option
   to execute tests in a random order.
 
+* The :option:`test --parallel` option now supports the value ``auto`` to run
+  one test process for each processor core.
+
 URLs
 ~~~~
 

tests/runtests.py

@@ -23,7 +23,7 @@ else:
     from django.conf import settings
     from django.db import connection, connections
     from django.test import TestCase, TransactionTestCase
-    from django.test.runner import default_test_processes
+    from django.test.runner import parallel_type
     from django.test.selenium import SeleniumTestCaseBase
     from django.test.utils import NullTimeKeeper, TimeKeeper, get_runner
     from django.utils.deprecation import (
@@ -329,7 +329,7 @@ def actual_test_processes(parallel):
     if parallel == 0:
         # This doesn't work before django.setup() on some databases.
         if all(conn.features.can_clone_databases for conn in connections.all()):
-            return default_test_processes()
+            return parallel_type('auto')
         else:
             return 1
     else:
@@ -354,11 +354,12 @@ def django_tests(verbosity, interactive, failfast, keepdb, reverse,
                  test_labels, debug_sql, parallel, tags, exclude_tags,
                  test_name_patterns, start_at, start_after, pdb, buffer,
                  timing, shuffle):
+    actual_parallel = actual_test_processes(parallel)
+
     if verbosity >= 1:
         msg = "Testing against Django installed in '%s'" % os.path.dirname(django.__file__)
-        max_parallel = default_test_processes() if parallel == 0 else parallel
-        if max_parallel > 1:
-            msg += " with up to %d processes" % max_parallel
+        if actual_parallel > 1:
+            msg += " with up to %d processes" % actual_parallel
         print(msg)
 
     test_labels, state = setup_run_tests(verbosity, start_at, start_after, test_labels)
@@ -373,7 +374,7 @@ def django_tests(verbosity, interactive, failfast, keepdb, reverse,
         keepdb=keepdb,
         reverse=reverse,
         debug_sql=debug_sql,
-        parallel=actual_test_processes(parallel),
+        parallel=actual_parallel,
         tags=tags,
         exclude_tags=exclude_tags,
         test_name_patterns=test_name_patterns,
@@ -562,10 +563,18 @@ if __name__ == "__main__":
         '--debug-sql', action='store_true',
         help='Turn on the SQL query logger within tests.',
     )
+    try:
+        default_parallel = int(os.environ['DJANGO_TEST_PROCESSES'])
+    except KeyError:
+        # actual_test_processes() converts this to "auto" later on.
+        default_parallel = 0
     parser.add_argument(
-        '--parallel', nargs='?', default=0, type=int,
-        const=default_test_processes(), metavar='N',
-        help='Run tests using up to N parallel processes.',
+        '--parallel', nargs='?', const='auto', default=default_parallel,
+        type=parallel_type, metavar='N',
+        help=(
+            'Run tests using up to N parallel processes. Use the value "auto" '
+            'to run one test process for each processor core.'
+        ),
     )
     parser.add_argument(
         '--tag', dest='tags', action='append',

tests/test_runner/test_discover_runner.py

@@ -50,16 +50,31 @@ class DiscoverRunnerParallelArgumentTests(SimpleTestCase):
 
     def test_parallel_default(self, *mocked_objects):
         result = self.get_parser().parse_args([])
-        self.assertEqual(result.parallel, 1)
+        self.assertEqual(result.parallel, 0)
 
     def test_parallel_flag(self, *mocked_objects):
         result = self.get_parser().parse_args(['--parallel'])
         self.assertEqual(result.parallel, 12)
 
+    def test_parallel_auto(self, *mocked_objects):
+        result = self.get_parser().parse_args(['--parallel', 'auto'])
+        self.assertEqual(result.parallel, 12)
+
     def test_parallel_count(self, *mocked_objects):
         result = self.get_parser().parse_args(['--parallel', '17'])
         self.assertEqual(result.parallel, 17)
 
+    def test_parallel_invalid(self, *mocked_objects):
+        with self.assertRaises(SystemExit), captured_stderr() as stderr:
+            self.get_parser().parse_args(['--parallel', 'unaccepted'])
+        msg = "argument --parallel: 'unaccepted' is not an integer or the string 'auto'"
+        self.assertIn(msg, stderr.getvalue())
+
+    @mock.patch.dict(os.environ, {'DJANGO_TEST_PROCESSES': '7'})
+    def test_parallel_env_var(self, *mocked_objects):
+        result = self.get_parser().parse_args([])
+        self.assertEqual(result.parallel, 7)
+
     @mock.patch.dict(os.environ, {'DJANGO_TEST_PROCESSES': 'typo'})
     def test_parallel_env_var_non_int(self, *mocked_objects):
         with self.assertRaises(ValueError):