# Django 4.2.11 documentation

# Source code for django.test.runner

    import argparse
    import ctypes
    import faulthandler
    import io
    import itertools
    import logging
    import multiprocessing
    import os
    import pickle
    import random
    import sys
    import textwrap
    import unittest
    import warnings
    from collections import defaultdict
    from contextlib import contextmanager
    from importlib import import_module
    from io import StringIO

    import sqlparse

    import django
    from django.core.management import call_command
    from django.db import connections
    from django.test import SimpleTestCase, TestCase
    from django.test.utils import NullTimeKeeper, TimeKeeper, iter_test_cases
    from django.test.utils import setup_databases as _setup_databases
    from django.test.utils import setup_test_environment
    from django.test.utils import teardown_databases as _teardown_databases
    from django.test.utils import teardown_test_environment
    from django.utils.crypto import new_hash
    from django.utils.datastructures import OrderedSet
    from django.utils.deprecation import RemovedInDjango50Warning

    try:
        import ipdb as pdb
    except ImportError:
        import pdb

    try:
        import tblib.pickling_support
    except ImportError:
        tblib = None

    class DebugSQLTextTestResult(unittest.TextTestResult):
        def __init__(self, stream, descriptions, verbosity):
            self.logger = logging.getLogger("django.db.backends")
            self.logger.setLevel(logging.DEBUG)
            self.debug_sql_stream = None
            super().__init__(stream, descriptions, verbosity)

        def startTest(self, test):
            self.debug_sql_stream = StringIO()
            self.handler = logging.StreamHandler(self.debug_sql_stream)
            self.logger.addHandler(self.handler)
            super().startTest(test)

        def stopTest(self, test):
            super().stopTest(test)
            self.logger.removeHandler(self.handler)
            if self.showAll:
                self.debug_sql_stream.seek(0)
                self.stream.write(self.debug_sql_stream.read())
                self.stream.writeln(self.separator2)

        def addError(self, test, err):
            super().addError(test, err)
            if self.debug_sql_stream is None:
                # Error before tests e.g. in setUpTestData().
                sql = ""
            else:
                self.debug_sql_stream.seek(0)
                sql = self.debug_sql_stream.read()
            self.errors[-1] = self.errors[-1] + (sql,)

        def addFailure(self, test, err):
            super().addFailure(test, err)
            self.debug_sql_stream.seek(0)
            self.failures[-1] = self.failures[-1] + (self.debug_sql_stream.read(),)

        def addSubTest(self, test, subtest, err):
            super().addSubTest(test, subtest, err)
            if err is not None:
                self.debug_sql_stream.seek(0)
                errors = (
                    self.failures
                    if issubclass(err[0], test.failureException)
                    else self.errors
                )
                errors[-1] = errors[-1] + (self.debug_sql_stream.read(),)

        def printErrorList(self, flavour, errors):
            for test, err, sql_debug in errors:
                self.stream.writeln(self.separator1)
                self.stream.writeln("%s: %s" % (flavour, self.getDescription(test)))
                self.stream.writeln(self.separator2)
                self.stream.writeln(err)
                self.stream.writeln(self.separator2)
                self.stream.writeln(
                    sqlparse.format(sql_debug, reindent=True, keyword_case="upper")
                )

    class PDBDebugResult(unittest.TextTestResult):
        """
        Custom result class that triggers a PDB session when an error or failure
        occurs.
        """

        def addError(self, test, err):
            super().addError(test, err)
            self.debug(err)

        def addFailure(self, test, err):
            super().addFailure(test, err)
            self.debug(err)

        def addSubTest(self, test, subtest, err):
            if err is not None:
                self.debug(err)
            super().addSubTest(test, subtest, err)

        def debug(self, error):
            self._restoreStdout()
            self.buffer = False
            exc_type, exc_value, traceback = error
            print("\nOpening PDB: %r" % exc_value)
            pdb.post_mortem(traceback)

    class DummyList:
        """
        Dummy list class for faking storage of results in unittest.TestResult.
        """

        __slots__ = ()

        def append(self, item):
            pass

    class RemoteTestResult(unittest.TestResult):
        """
        Extend unittest.TestResult to record events in the child processes so they
        can be replayed in the parent process. Events include things like which
        tests succeeded or failed.
        """

        def __init__(self, *args, **kwargs):
            super().__init__(*args, **kwargs)
            # Fake storage of results to reduce memory usage. These are used by the
            # unittest default methods, but here 'events' is used instead.
            dummy_list = DummyList()
            self.failures = dummy_list
            self.errors = dummy_list
            self.skipped = dummy_list
            self.expectedFailures = dummy_list
            self.unexpectedSuccesses = dummy_list

            if tblib is not None:
                tblib.pickling_support.install()
            self.events = []

        def __getstate__(self):
            # Make this class picklable by removing the file-like buffer
            # attributes. This is possible since they aren't used after unpickling
            # after being sent to ParallelTestSuite.
            state = self.__dict__.copy()
            state.pop("_stdout_buffer", None)
            state.pop("_stderr_buffer", None)
            state.pop("_original_stdout", None)
            state.pop("_original_stderr", None)
            return state

        @property
        def test_index(self):
            return self.testsRun - 1

        def _confirm_picklable(self, obj):
            """
            Confirm that obj can be pickled and unpickled as multiprocessing will
            need to pickle the exception in the child process and unpickle it in
            the parent process. Let the exception rise, if not.
            """
            pickle.loads(pickle.dumps(obj))

        def _print_unpicklable_subtest(self, test, subtest, pickle_exc):
            print(
                """
    Subtest failed:

        test: {}
     subtest: {}

    Unfortunately, the subtest that failed cannot be pickled, so the parallel
    test runner cannot handle it cleanly. Here is the pickling error:

    > {}

    You should re-run this test with --parallel=1 to reproduce the failure
    with a cleaner failure message.
    """.format(
                    test, subtest, pickle_exc
                )
            )

        def check_picklable(self, test, err):
            # Ensure that sys.exc_info() tuples are picklable. This displays a
            # clear multiprocessing.pool.RemoteTraceback generated in the child
            # process instead of a multiprocessing.pool.MaybeEncodingError, making
            # the root cause easier to figure out for users who aren't familiar
            # with the multiprocessing module. Since we're in a forked process,
            # our best chance to communicate with them is to print to stdout.
            try:
                self._confirm_picklable(err)
            except Exception as exc:
                original_exc_txt = repr(err[1])
                original_exc_txt = textwrap.fill(
                    original_exc_txt, 75, initial_indent="    ", subsequent_indent="    "
                )
                pickle_exc_txt = repr(exc)
                pickle_exc_txt = textwrap.fill(
                    pickle_exc_txt, 75, initial_indent="    ", subsequent_indent="    "
                )
                if tblib is None:
                    print(
                        """

    {} failed:

    {}

    Unfortunately, tracebacks cannot be pickled, making it impossible for the
    parallel test runner to handle this exception cleanly.

    In order to see the traceback, you should install tblib:

        python -m pip install tblib
    """.format(
                            test, original_exc_txt
                        )
                    )
                else:
                    print(
                        """

    {} failed:

    {}

    Unfortunately, the exception it raised cannot be pickled, making it impossible
    for the parallel test runner to handle it cleanly.

    Here's the error encountered while trying to pickle the exception:

    {}

    You should re-run this test with the --parallel=1 option to reproduce the
    failure and get a correct traceback.
    """.format(
                            test, original_exc_txt, pickle_exc_txt
                        )
                    )
                raise

        def check_subtest_picklable(self, test, subtest):
            try:
                self._confirm_picklable(subtest)
            except Exception as exc:
                self._print_unpicklable_subtest(test, subtest, exc)
                raise

        def startTestRun(self):
            super().startTestRun()
            self.events.append(("startTestRun",))

        def stopTestRun(self):
            super().stopTestRun()
            self.events.append(("stopTestRun",))

        def startTest(self, test):
            super().startTest(test)
            self.events.append(("startTest", self.test_index))

        def stopTest(self, test):
            super().stopTest(test)
            self.events.append(("stopTest", self.test_index))

        def addError(self, test, err):
            self.check_picklable(test, err)
            self.events.append(("addError", self.test_index, err))
            super().addError(test, err)

        def addFailure(self, test, err):
            self.check_picklable(test, err)
            self.events.append(("addFailure", self.test_index, err))
            super().addFailure(test, err)

        def addSubTest(self, test, subtest, err):
            # Follow Python's implementation of unittest.TestResult.addSubTest() by
            # not doing anything when a subtest is successful.
            if err is not None:
                # Call check_picklable() before check_subtest_picklable() since
                # check_picklable() performs the tblib check.
                self.check_picklable(test, err)
                self.check_subtest_picklable(test, subtest)
                self.events.append(("addSubTest", self.test_index, subtest, err))
            super().addSubTest(test, subtest, err)

        def addSuccess(self, test):
            self.events.append(("addSuccess", self.test_index))
            super().addSuccess(test)

        def addSkip(self, test, reason):
            self.events.append(("addSkip", self.test_index, reason))
            super().addSkip(test, reason)

        def addExpectedFailure(self, test, err):
            # If tblib isn't installed, pickling the traceback will always fail.
            # However we don't want tblib to be required for running the tests
            # when they pass or fail as expected. Drop the traceback when an
            # expected failure occurs.
            if tblib is None:
                err = err[0], err[1], None
            self.check_picklable(test, err)
            self.events.append(("addExpectedFailure", self.test_index, err))
            super().addExpectedFailure(test, err)

        def addUnexpectedSuccess(self, test):
            self.events.append(("addUnexpectedSuccess", self.test_index))
            super().addUnexpectedSuccess(test)

        def wasSuccessful(self):
            """Tells whether or not this result was a success."""
            failure_types = {"addError", "addFailure", "addSubTest", "addUnexpectedSuccess"}
            return all(e[0] not in failure_types for e in self.events)

        def _exc_info_to_string(self, err, test):
            # Make this method no-op. It only powers the default unittest behavior
            # for recording errors, but this class pickles errors into 'events'
            # instead.
            return ""

    class RemoteTestRunner:
        """
        Run tests and record everything but don't display anything.

        The implementation matches the unpythonic coding style of unittest2.
        """

        resultclass = RemoteTestResult

        def __init__(self, failfast=False, resultclass=None, buffer=False):
            self.failfast = failfast
            self.buffer = buffer
            if resultclass is not None:
                self.resultclass = resultclass

        def run(self, test):
            result = self.resultclass()
            unittest.registerResult(result)
            result.failfast = self.failfast
            result.buffer = self.buffer
            test(result)
            return result

    def get_max_test_processes():
        """
        The maximum number of test processes when using the --parallel option.
        """
        # The current implementation of the parallel test runner requires
        # multiprocessing to start subprocesses with fork() or spawn().
        if multiprocessing.get_start_method() not in {"fork", "spawn"}:
            return 1
        try:
            return int(os.environ["DJANGO_TEST_PROCESSES"])
        except KeyError:
            return multiprocessing.cpu_count()

    def parallel_type(value):
        """Parse value passed to the --parallel option."""
        if value == "auto":
            return value
        try:
            return int(value)
        except ValueError:
            raise argparse.ArgumentTypeError(
                f"{value!r} is not an integer or the string 'auto'"
            )

    _worker_id = 0

    def _init_worker(
        counter,
        initial_settings=None,
        serialized_contents=None,
        process_setup=None,
        process_setup_args=None,
        debug_mode=None,
    ):
        """
        Switch to databases dedicated to this worker.

        This helper lives at module-level because of the multiprocessing module's
        requirements.
        """

        global _worker_id

        with counter.get_lock():
            counter.value += 1
            _worker_id = counter.value

        start_method = multiprocessing.get_start_method()

        if start_method == "spawn":
            if process_setup and callable(process_setup):
                if process_setup_args is None:
                    process_setup_args = ()
                process_setup(*process_setup_args)
            django.setup()
            setup_test_environment(debug=debug_mode)

        for alias in connections:
            connection = connections[alias]
            if start_method == "spawn":
                # Restore initial settings in spawned processes.
                connection.settings_dict.update(initial_settings[alias])
                if value := serialized_contents.get(alias):
                    connection._test_serialized_contents = value
            connection.creation.setup_worker_connection(_worker_id)

    def _run_subsuite(args):
        """
        Run a suite of tests with a RemoteTestRunner and return a RemoteTestResult.

        This helper lives at module-level and its arguments are wrapped in a tuple
        because of the multiprocessing module's requirements.
        """
        runner_class, subsuite_index, subsuite, failfast, buffer = args
        runner = runner_class(failfast=failfast, buffer=buffer)
        result = runner.run(subsuite)
        return subsuite_index, result.events

    def _process_setup_stub(*args):
        """Stub method to simplify run() implementation."""
        pass

    class ParallelTestSuite(unittest.TestSuite):
        """
        Run a series of tests in parallel in several processes.

        While the unittest module's documentation implies that orchestrating the
        execution of tests is the responsibility of the test runner, in practice,
        it appears that TestRunner classes are more concerned with formatting and
        displaying test results.

        Since there are fewer use cases for customizing TestSuite than TestRunner,
        implementing parallelization at the level of the TestSuite improves
        interoperability with existing custom test runners. A single instance of a
        test runner can still collect results from all tests without being aware
        that they have been run in parallel.
        """

        # In case someone wants to modify these in a subclass.
        init_worker = _init_worker
        process_setup = _process_setup_stub
        process_setup_args = ()
        run_subsuite = _run_subsuite
        runner_class = RemoteTestRunner

        def __init__(
            self, subsuites, processes, failfast=False, debug_mode=False, buffer=False
        ):
            self.subsuites = subsuites
            self.processes = processes
            self.failfast = failfast
            self.debug_mode = debug_mode
            self.buffer = buffer
            self.initial_settings = None
            self.serialized_contents = None
            super().__init__()

        def run(self, result):
            """
            Distribute test cases across workers.

            Return an identifier of each test case with its result in order to use
            imap_unordered to show results as soon as they're available.

            To minimize pickling errors when getting results from workers:

            - pass back numeric indexes in self.subsuites instead of tests
            - make tracebacks picklable with tblib, if available

            Even with tblib, errors may still occur for dynamically created
            exception classes which cannot be unpickled.
            """
            self.initialize_suite()
            counter = multiprocessing.Value(ctypes.c_int, 0)
            pool = multiprocessing.Pool(
                processes=self.processes,
                initializer=self.init_worker.__func__,
                initargs=[
                    counter,
                    self.initial_settings,
                    self.serialized_contents,
                    self.process_setup.__func__,
                    self.process_setup_args,
                    self.debug_mode,
                ],
            )
            args = [
                (self.runner_class, index, subsuite, self.failfast, self.buffer)
                for index, subsuite in enumerate(self.subsuites)
            ]
            test_results = pool.imap_unordered(self.run_subsuite.__func__, args)

            while True:
                if result.shouldStop:
                    pool.terminate()
                    break

                try:
                    subsuite_index, events = test_results.next(timeout=0.1)
                except multiprocessing.TimeoutError:
                    continue
                except StopIteration:
                    pool.close()
                    break

                tests = list(self.subsuites[subsuite_index])
                for event in events:
                    event_name = event[0]
                    handler = getattr(result, event_name, None)
                    if handler is None:
                        continue
                    test = tests[event[1]]
                    args = event[2:]
                    handler(test, *args)

            pool.join()

            return result

        def __iter__(self):
            return iter(self.subsuites)

        def initialize_suite(self):
            if multiprocessing.get_start_method() == "spawn":
                self.initial_settings = {
                    alias: connections[alias].settings_dict for alias in connections
                }
                self.serialized_contents = {
                    alias: connections[alias]._test_serialized_contents
                    for alias in connections
                    if alias in self.serialized_aliases
                }

    class Shuffler:
        """
        This class implements shuffling with a special consistency property.
        Consistency means that, for a given seed and key function, if two sets of
        items are shuffled, the resulting order will agree on the intersection of
        the two sets. For example, if items are removed from an original set, the
        shuffled order for the new set will be the shuffled order of the original
        set restricted to the smaller set.
        """

        # This doesn't need to be cryptographically strong, so use what's fastest.
        hash_algorithm = "md5"

        @classmethod
        def _hash_text(cls, text):
            h = new_hash(cls.hash_algorithm, usedforsecurity=False)
            h.update(text.encode("utf-8"))
            return h.hexdigest()

        def __init__(self, seed=None):
            if seed is None:
                # Limit seeds to 10 digits for simpler output.
                seed = random.randint(0, 10**10 - 1)
                seed_source = "generated"
            else:
                seed_source = "given"
            self.seed = seed
            self.seed_source = seed_source

        @property
        def seed_display(self):
            return f"{self.seed!r} ({self.seed_source})"

        def _hash_item(self, item, key):
            text = "{}{}".format(self.seed, key(item))
            return self._hash_text(text)

        def shuffle(self, items, key):
            """
            Return a new list of the items in a shuffled order.

            The `key` is a function that accepts an item in `items` and returns
            a string unique for that item that can be viewed as a string id. The
            order of the return value is deterministic. It depends on the seed
            and key function but not on the original order.
            """
            hashes = {}
            for item in items:
                hashed = self._hash_item(item, key)
                if hashed in hashes:
                    msg = "item {!r} has same hash {!r} as item {!r}".format(
                        item,
                        hashed,
                        hashes[hashed],
                    )
                    raise RuntimeError(msg)
                hashes[hashed] = item
            return [hashes[hashed] for hashed in sorted(hashes)]

    class DiscoverRunner:
        """A Django test runner that uses unittest2 test discovery."""

        test_suite = unittest.TestSuite
        parallel_test_suite = ParallelTestSuite
        test_runner = unittest.TextTestRunner
        test_loader = unittest.defaultTestLoader
        reorder_by = (TestCase, SimpleTestCase)

        def __init__(
            self,
            pattern=None,
            top_level=None,
            verbosity=1,
            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,
            buffer=False,
            enable_faulthandler=True,
            timing=False,
            shuffle=False,
            logger=None,
            **kwargs,
        ):
            self.pattern = pattern
            self.top_level = top_level
            self.verbosity = verbosity
            self.interactive = interactive
            self.failfast = failfast
            self.keepdb = keepdb
            self.reverse = reverse
            self.debug_mode = debug_mode
            self.debug_sql = debug_sql
            self.parallel = parallel
            self.tags = set(tags or [])
            self.exclude_tags = set(exclude_tags or [])
            if not faulthandler.is_enabled() and enable_faulthandler:
                try:
                    faulthandler.enable(file=sys.stderr.fileno())
                except (AttributeError, io.UnsupportedOperation):
                    faulthandler.enable(file=sys.__stderr__.fileno())
            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
            self.test_name_patterns = None
            self.time_keeper = TimeKeeper() if timing else NullTimeKeeper()
            if test_name_patterns:
                # unittest does not export the _convert_select_pattern function
                # that converts command-line arguments to patterns.
                self.test_name_patterns = {
                    pattern if "*" in pattern else "*%s*" % pattern
                    for pattern in test_name_patterns
                }
            self.shuffle = shuffle
            self._shuffler = None
            self.logger = logger

        @classmethod
        def add_arguments(cls, parser):
            parser.add_argument(
                "-t",
                "--top-level-directory",
                dest="top_level",
                help="Top level of project for unittest discovery.",
            )
            parser.add_argument(
                "-p",
                "--pattern",
                default="test*.py",
                help="The test matching pattern. Defaults to test*.py.",
            )
            parser.add_argument(
                "--keepdb", action="store_true", help="Preserves the test DB between runs."
            )
            parser.add_argument(
                "--shuffle",
                nargs="?",
                default=False,
                type=int,
                metavar="SEED",
                help="Shuffles test case order.",
            )
            parser.add_argument(
                "-r",
                "--reverse",
                action="store_true",
                help="Reverses test case order.",
            )
            parser.add_argument(
                "--debug-mode",
                action="store_true",
                help="Sets settings.DEBUG to True.",
            )
            parser.add_argument(
                "-d",
                "--debug-sql",
                action="store_true",
                help="Prints logged SQL queries on failure.",
            )
            parser.add_argument(
                "--parallel",
                nargs="?",
                const="auto",
                default=0,
                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",
                help="Run only tests with the specified tag. Can be used multiple times.",
            )
            parser.add_argument(
                "--exclude-tag",
                action="append",
                dest="exclude_tags",
                help="Do not run tests with the specified tag. Can be used multiple times.",
            )
            parser.add_argument(
                "--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.",
            )
            parser.add_argument(
                "--no-faulthandler",
                action="store_false",
                dest="enable_faulthandler",
                help="Disables the Python faulthandler module during tests.",
            )
            parser.add_argument(
                "--timing",
                action="store_true",
                help=("Output timings, including database set up and total run time."),
            )
            parser.add_argument(
                "-k",
                action="append",
                dest="test_name_patterns",
                help=(
                    "Only run test methods and classes that match the pattern "
                    "or substring. Can be used multiple times. Same as "
                    "unittest -k option."
                ),
            )

        @property
        def shuffle_seed(self):
            if self._shuffler is None:
                return None
            return self._shuffler.seed

        def log(self, msg, level=None):
            """
            Log the message at the given logging level (the default is INFO).

            If a logger isn't set, the message is instead printed to the console,
            respecting the configured verbosity. A verbosity of 0 prints no output,
            a verbosity of 1 prints INFO and above, and a verbosity of 2 or higher
            prints all levels.
            """
            if level is None:
                level = logging.INFO
            if self.logger is None:
                if self.verbosity <= 0 or (self.verbosity == 1 and level < logging.INFO):
                    return
                print(msg)
            else:
                self.logger.log(level, msg)

        def setup_test_environment(self, **kwargs):
            setup_test_environment(debug=self.debug_mode)
            unittest.installHandler()

        def setup_shuffler(self):
            if self.shuffle is False:
                return
            shuffler = Shuffler(seed=self.shuffle)
            self.log(f"Using shuffle seed: {shuffler.seed_display}")
            self._shuffler = shuffler

        @contextmanager
        def load_with_patterns(self):
            original_test_name_patterns = self.test_loader.testNamePatterns
            self.test_loader.testNamePatterns = self.test_name_patterns
            try:
                yield
            finally:
                # Restore the original patterns.
                self.test_loader.testNamePatterns = original_test_name_patterns

        def load_tests_for_label(self, label, discover_kwargs):
            label_as_path = os.path.abspath(label)
            tests = None

            # If a module, or "module.ClassName[.method_name]", just run those.
            if not os.path.exists(label_as_path):
                with self.load_with_patterns():
                    tests = self.test_loader.loadTestsFromName(label)
                if tests.countTestCases():
                    return tests
            # Try discovery if "label" is a package or directory.
            is_importable, is_package = try_importing(label)
            if is_importable:
                if not is_package:
                    return tests
            elif not os.path.isdir(label_as_path):
                if os.path.exists(label_as_path):
                    assert tests is None
                    raise RuntimeError(
                        f"One of the test labels is a path to a file: {label!r}, "
                        f"which is not supported. Use a dotted module name or "
                        f"path to a directory instead."
                    )
                return tests

            kwargs = discover_kwargs.copy()
            if os.path.isdir(label_as_path) and not self.top_level:
                kwargs["top_level_dir"] = find_top_level(label_as_path)

            with self.load_with_patterns():
                tests = self.test_loader.discover(start_dir=label, **kwargs)

            # Make unittest forget the top-level dir it calculated from this run,
            # to support running tests from two different top-levels.
            self.test_loader._top_level_dir = None
            return tests

        def build_suite(self, test_labels=None, extra_tests=None, **kwargs):
            if extra_tests is not None:
                warnings.warn(
                    "The extra_tests argument is deprecated.",
                    RemovedInDjango50Warning,
                    stacklevel=2,
                )
            test_labels = test_labels or ["."]
            extra_tests = extra_tests or []

            discover_kwargs = {}
            if self.pattern is not None:
                discover_kwargs["pattern"] = self.pattern
            if self.top_level is not None:
                discover_kwargs["top_level_dir"] = self.top_level
            self.setup_shuffler()

            all_tests = []
            for label in test_labels:
                tests = self.load_tests_for_label(label, discover_kwargs)
                all_tests.extend(iter_test_cases(tests))

            all_tests.extend(iter_test_cases(extra_tests))

            if self.tags or self.exclude_tags:
                if self.tags:
                    self.log(
                        "Including test tag(s): %s." % ", ".join(sorted(self.tags)),
                        level=logging.DEBUG,
                    )
                if self.exclude_tags:
                    self.log(
                        "Excluding test tag(s): %s." % ", ".join(sorted(self.exclude_tags)),
                        level=logging.DEBUG,
                    )
                all_tests = filter_tests_by_tags(all_tests, self.tags, self.exclude_tags)

            # Put the failures detected at load time first for quicker feedback.
            # _FailedTest objects include things like test modules that couldn't be
            # found or that couldn't be loaded due to syntax errors.
            test_types = (unittest.loader._FailedTest, *self.reorder_by)
            all_tests = list(
                reorder_tests(
                    all_tests,
                    test_types,
                    shuffler=self._shuffler,
                    reverse=self.reverse,
                )
            )
            self.log("Found %d test(s)." % len(all_tests))
            suite = self.test_suite(all_tests)

            if self.parallel > 1:
                subsuites = partition_suite_by_case(suite)
                # Since tests are distributed across processes on a per-TestCase
                # basis, there's no need for more processes than TestCases.
                processes = min(self.parallel, len(subsuites))
                # Update also "parallel" because it's used to determine the number
                # of test databases.
                self.parallel = processes
                if processes > 1:
                    suite = self.parallel_test_suite(
                        subsuites,
                        processes,
                        self.failfast,
                        self.debug_mode,
                        self.buffer,
                    )
            return suite

        def setup_databases(self, **kwargs):
            return _setup_databases(
                self.verbosity,
                self.interactive,
                time_keeper=self.time_keeper,
                keepdb=self.keepdb,
                debug_sql=self.debug_sql,
                parallel=self.parallel,
                **kwargs,
            )

        def get_resultclass(self):
            if self.debug_sql:
                return DebugSQLTextTestResult
            elif self.pdb:
                return PDBDebugResult

        def get_test_runner_kwargs(self):
            return {
                "failfast": self.failfast,
                "resultclass": self.get_resultclass(),
                "verbosity": self.verbosity,
                "buffer": self.buffer,
            }

        def run_checks(self, databases):
            # Checks are run after database creation since some checks require
            # database access.
            call_command("check", verbosity=self.verbosity, databases=databases)

        def run_suite(self, suite, **kwargs):
            kwargs = self.get_test_runner_kwargs()
            runner = self.test_runner(**kwargs)
            try:
                return runner.run(suite)
            finally:
                if self._shuffler is not None:
                    seed_display = self._shuffler.seed_display
                    self.log(f"Used shuffle seed: {seed_display}")

        def teardown_databases(self, old_config, **kwargs):
            """Destroy all the non-mirror databases."""
            _teardown_databases(
                old_config,
                verbosity=self.verbosity,
                parallel=self.parallel,
                keepdb=self.keepdb,
            )

        def teardown_test_environment(self, **kwargs):
            unittest.removeHandler()
            teardown_test_environment()

        def suite_result(self, suite, result, **kwargs):
            return (
                len(result.failures) + len(result.errors) + len(result.unexpectedSuccesses)
            )

        def _get_databases(self, suite):
            databases = {}
            for test in iter_test_cases(suite):
                test_databases = getattr(test, "databases", None)
                if test_databases == "__all__":
                    test_databases = connections
                if test_databases:
                    serialized_rollback = getattr(test, "serialized_rollback", False)
                    databases.update(
                        (alias, serialized_rollback or databases.get(alias, False))
                        for alias in test_databases
                    )
            return databases

        def get_databases(self, suite):
            databases = self._get_databases(suite)
            unused_databases = [alias for alias in connections if alias not in databases]
            if unused_databases:
                self.log(
                    "Skipping setup of unused database(s): %s."
                    % ", ".join(sorted(unused_databases)),
                    level=logging.DEBUG,
                )
            return databases

        def run_tests(self, test_labels, extra_tests=None, **kwargs):
            """
            Run the unit tests for all the test labels in the provided list.

            Test labels should be dotted Python paths to test modules, test
            classes, or test methods.

            Return the number of tests that failed.
            """
            if extra_tests is not None:
                warnings.warn(
                    "The extra_tests argument is deprecated.",
                    RemovedInDjango50Warning,
                    stacklevel=2,
                )
            self.setup_test_environment()
            suite = self.build_suite(test_labels, extra_tests)
            databases = self.get_databases(suite)
            suite.serialized_aliases = set(
                alias for alias, serialize in databases.items() if serialize
            )
            with self.time_keeper.timed("Total database setup"):
                old_config = self.setup_databases(
                    aliases=databases,
                    serialized_aliases=suite.serialized_aliases,
                )
            run_failed = False
            try:
                self.run_checks(databases)
                result = self.run_suite(suite)
            except Exception:
                run_failed = True
                raise
            finally:
                try:
                    with self.time_keeper.timed("Total database teardown"):
                        self.teardown_databases(old_config)
                    self.teardown_test_environment()
                except Exception:
                    # Silence teardown exceptions if an exception was raised during
                    # runs to avoid shadowing it.
                    if not run_failed:
                        raise
            self.time_keeper.print_results()
            return self.suite_result(suite, result)

    def try_importing(label):
        """
        Try importing a test label, and return (is_importable, is_package).

        Relative labels like "." and ".." are seen as directories.
        """
        try:
            mod = import_module(label)
        except (ImportError, TypeError):
            return (False, False)

        return (True, hasattr(mod, "__path__"))

    def find_top_level(top_level):
        # Try to be a bit smarter than unittest about finding the default top-level
        # for a given directory path, to avoid breaking relative imports.
        # (Unittest's default is to set top-level equal to the path, which means
        # relative imports will result in "Attempted relative import in
        # non-package.").

        # We'd be happy to skip this and require dotted module paths (which don't
        # cause this problem) instead of file paths (which do), but in the case of
        # a directory in the cwd, which would be equally valid if considered as a
        # top-level module or as a directory path, unittest unfortunately prefers
        # the latter.
        while True:
            init_py = os.path.join(top_level, "__init__.py")
            if not os.path.exists(init_py):
                break
            try_next = os.path.dirname(top_level)
            if try_next == top_level:
                # __init__.py all the way down? give up.
                break
            top_level = try_next
        return top_level

    def _class_shuffle_key(cls):
        return f"{cls.__module__}.{cls.__qualname__}"

    def shuffle_tests(tests, shuffler):
        """
        Return an iterator over the given tests in a shuffled order, keeping tests
        next to other tests of their class.

        `tests` should be an iterable of tests.
        """
        tests_by_type = {}
        for _, class_tests in itertools.groupby(tests, type):
            class_tests = list(class_tests)
            test_type = type(class_tests[0])
            class_tests = shuffler.shuffle(class_tests, key=lambda test: test.id())
            tests_by_type[test_type] = class_tests

        classes = shuffler.shuffle(tests_by_type, key=_class_shuffle_key)

        return itertools.chain(*(tests_by_type[cls] for cls in classes))

    def reorder_test_bin(tests, shuffler=None, reverse=False):
        """
        Return an iterator that reorders the given tests, keeping tests next to
        other tests of their class.

        `tests` should be an iterable of tests that supports reversed().
        """
        if shuffler is None:
            if reverse:
                return reversed(tests)
            # The function must return an iterator.
            return iter(tests)

        tests = shuffle_tests(tests, shuffler)
        if not reverse:
            return tests
        # Arguments to reversed() must be reversible.
        return reversed(list(tests))

    def reorder_tests(tests, classes, reverse=False, shuffler=None):
        """
        Reorder an iterable of tests, grouping by the given TestCase classes.

        This function also removes any duplicates and reorders so that tests of the
        same type are consecutive.

        The result is returned as an iterator. `classes` is a sequence of types.
        Tests that are instances of `classes[0]` are grouped first, followed by
        instances of `classes[1]`, etc. Tests that are not instances of any of the
        classes are grouped last.

        If `reverse` is True, the tests within each `classes` group are reversed,
        but without reversing the order of `classes` itself.

        The `shuffler` argument is an optional instance of this module's `Shuffler`
        class. If provided, tests will be shuffled within each `classes` group, but
        keeping tests with other tests of their TestCase class. Reversing is
        applied after shuffling to allow reversing the same random order.
        """
        # Each bin maps TestCase class to OrderedSet of tests. This permits tests
        # to be grouped by TestCase class even if provided non-consecutively.
        bins = [defaultdict(OrderedSet) for i in range(len(classes) + 1)]
        *class_bins, last_bin = bins

        for test in tests:
            for test_bin, test_class in zip(class_bins, classes):
                if isinstance(test, test_class):
                    break
            else:
                test_bin = last_bin
            test_bin[type(test)].add(test)

        for test_bin in bins:
            # Call list() since reorder_test_bin()'s input must support reversed().
            tests = list(itertools.chain.from_iterable(test_bin.values()))
            yield from reorder_test_bin(tests, shuffler=shuffler, reverse=reverse)

    def partition_suite_by_case(suite):
        """Partition a test suite by test case, preserving the order of tests."""
        suite_class = type(suite)
        all_tests = iter_test_cases(suite)
        return [suite_class(tests) for _, tests in itertools.groupby(all_tests, type)]

    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):
            test_fn = getattr(test, test_fn_name)
            test_fn_tags = list(getattr(test_fn, "tags", []))
            test_tags = test_tags.union(test_fn_tags)
        if tags and test_tags.isdisjoint(tags):
            return False
        return test_tags.isdisjoint(exclude_tags)

    def filter_tests_by_tags(tests, tags, exclude_tags):
        """Return the matching tests as an iterator."""
        return (test for test in tests if test_match_tags(test, tags, exclude_tags))