Fixed #27685 -- Added watchman support to the autoreloader.

Removed support for pyinotify (refs #9722).

6 files changed, 647 insertions, 210 deletions

diff --git a/tests/apps/tests.py b/tests/apps/tests.py
index cd22a4d45c..566aec60c3 100644
--- a/tests/apps/tests.py
+++ b/tests/apps/tests.py
@@ -48,6 +48,9 @@ class AppsTests(SimpleTestCase):
         self.assertIs(apps.ready, True)
         # Non-master app registries are populated in __init__.
         self.assertIs(Apps().ready, True)
+        # The condition is set when apps are ready
+        self.assertIs(apps.ready_event.is_set(), True)
+        self.assertIs(Apps().ready_event.is_set(), True)
 
     def test_bad_app_config(self):
         """
diff --git a/tests/i18n/tests.py b/tests/i18n/tests.py
index 7b54089cf2..2377c8992e 100644
--- a/tests/i18n/tests.py
+++ b/tests/i18n/tests.py
@@ -7,9 +7,12 @@ import re
 import tempfile
 from contextlib import contextmanager
 from importlib import import_module
+from pathlib import Path
 from threading import local
 from unittest import mock
 
+import _thread
+
 from django import forms
 from django.apps import AppConfig
 from django.conf import settings
@@ -33,6 +36,9 @@ from django.utils.translation import (
     npgettext, npgettext_lazy, pgettext, to_language, to_locale, trans_null,
     trans_real, ugettext, ugettext_lazy, ungettext, ungettext_lazy,
 )
+from django.utils.translation.reloader import (
+    translation_file_changed, watch_for_translation_changes,
+)
 
 from .forms import CompanyForm, I18nForm, SelectDateForm
 from .models import Company, TestModel
@@ -1790,3 +1796,65 @@ class NonDjangoLanguageTests(SimpleTestCase):
     def test_plural_non_django_language(self):
         self.assertEqual(get_language(), 'xyz')
         self.assertEqual(ngettext('year', 'years', 2), 'years')
+
+
+@override_settings(USE_I18N=True)
+class WatchForTranslationChangesTests(SimpleTestCase):
+    @override_settings(USE_I18N=False)
+    def test_i18n_disabled(self):
+        mocked_sender = mock.MagicMock()
+        watch_for_translation_changes(mocked_sender)
+        mocked_sender.watch_dir.assert_not_called()
+
+    def test_i18n_enabled(self):
+        mocked_sender = mock.MagicMock()
+        watch_for_translation_changes(mocked_sender)
+        self.assertGreater(mocked_sender.watch_dir.call_count, 1)
+
+    def test_i18n_locale_paths(self):
+        mocked_sender = mock.MagicMock()
+        with tempfile.TemporaryDirectory() as app_dir:
+            with self.settings(LOCALE_PATHS=[app_dir]):
+                watch_for_translation_changes(mocked_sender)
+            mocked_sender.watch_dir.assert_any_call(Path(app_dir), '**/*.mo')
+
+    def test_i18n_app_dirs(self):
+        mocked_sender = mock.MagicMock()
+        with self.settings(INSTALLED_APPS=['tests.i18n.sampleproject']):
+            watch_for_translation_changes(mocked_sender)
+        project_dir = Path(__file__).parent / 'sampleproject' / 'locale'
+        mocked_sender.watch_dir.assert_any_call(project_dir, '**/*.mo')
+
+    def test_i18n_local_locale(self):
+        mocked_sender = mock.MagicMock()
+        watch_for_translation_changes(mocked_sender)
+        locale_dir = Path(__file__).parent / 'locale'
+        mocked_sender.watch_dir.assert_any_call(locale_dir, '**/*.mo')
+
+
+class TranslationFileChangedTests(SimpleTestCase):
+    def setUp(self):
+        self.gettext_translations = gettext_module._translations.copy()
+        self.trans_real_translations = trans_real._translations.copy()
+
+    def tearDown(self):
+        gettext._translations = self.gettext_translations
+        trans_real._translations = self.trans_real_translations
+
+    def test_ignores_non_mo_files(self):
+        gettext_module._translations = {'foo': 'bar'}
+        path = Path('test.py')
+        self.assertIsNone(translation_file_changed(None, path))
+        self.assertEqual(gettext_module._translations, {'foo': 'bar'})
+
+    def test_resets_cache_with_mo_files(self):
+        gettext_module._translations = {'foo': 'bar'}
+        trans_real._translations = {'foo': 'bar'}
+        trans_real._default = 1
+        trans_real._active = False
+        path = Path('test.mo')
+        self.assertIs(translation_file_changed(None, path), True)
+        self.assertEqual(gettext_module._translations, {})
+        self.assertEqual(trans_real._translations, {})
+        self.assertIsNone(trans_real._default)
+        self.assertIsInstance(trans_real._active, _thread._local)
diff --git a/tests/requirements/py3.txt b/tests/requirements/py3.txt
index cc84522ca0..3f0a01e164 100644
--- a/tests/requirements/py3.txt
+++ b/tests/requirements/py3.txt
@@ -9,6 +9,7 @@ Pillow != 5.4.0
 pylibmc; sys.platform != 'win32'
 python-memcached >= 1.59
 pytz
+pywatchman; sys.platform != 'win32'
 PyYAML
 selenium
 sqlparse
diff --git a/tests/utils_tests/locale/nl/LC_MESSAGES/django.mo b/tests/utils_tests/locale/nl/LC_MESSAGES/django.mo
deleted file mode 100644
index 3ead8f2a31..0000000000
--- a/tests/utils_tests/locale/nl/LC_MESSAGES/django.mo
+++ /dev/null
diff --git a/tests/utils_tests/locale/nl/LC_MESSAGES/django.po b/tests/utils_tests/locale/nl/LC_MESSAGES/django.po
deleted file mode 100644
index 6633f12b39..0000000000
--- a/tests/utils_tests/locale/nl/LC_MESSAGES/django.po
+++ /dev/null
@@ -1,17 +0,0 @@
-# SOME DESCRIPTIVE TITLE.
-# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
-# This file is distributed under the same license as the PACKAGE package.
-# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
-#
-#, fuzzy
-msgid ""
-msgstr ""
-"Project-Id-Version: PACKAGE VERSION\n"
-"Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2007-09-15 19:15+0200\n"
-"PO-Revision-Date: 2010-05-12 12:41-0300\n"
-"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
-"Language-Team: LANGUAGE <LL@li.org>\n"
-"MIME-Version: 1.0\n"
-"Content-Type: text/plain; charset=UTF-8\n"
-"Content-Transfer-Encoding: 8bit\n"
diff --git a/tests/utils_tests/test_autoreload.py b/tests/utils_tests/test_autoreload.py
index 486d62cd18..6aa272dd9a 100644
--- a/tests/utils_tests/test_autoreload.py
+++ b/tests/utils_tests/test_autoreload.py
@@ -1,257 +1,279 @@
-import gettext
+import contextlib
 import os
+import py_compile
 import shutil
+import sys
 import tempfile
+import threading
+import time
+import zipfile
 from importlib import import_module
-from unittest import mock
+from pathlib import Path
+from unittest import mock, skip
 
-import _thread
-
-from django import conf
-from django.contrib import admin
-from django.test import SimpleTestCase, override_settings
+from django.apps.registry import Apps
+from django.test import SimpleTestCase
 from django.test.utils import extend_sys_path
 from django.utils import autoreload
-from django.utils.translation import trans_real
-
-LOCALE_PATH = os.path.join(os.path.dirname(__file__), 'locale')
+from django.utils.autoreload import WatchmanUnavailable
 
 
-class TestFilenameGenerator(SimpleTestCase):
+class TestIterModulesAndFiles(SimpleTestCase):
+    def import_and_cleanup(self, name):
+        import_module(name)
+        self.addCleanup(lambda: sys.path_importer_cache.clear())
+        self.addCleanup(lambda: sys.modules.pop(name, None))
 
     def clear_autoreload_caches(self):
-        autoreload._cached_modules = set()
-        autoreload._cached_filenames = []
+        autoreload.iter_modules_and_files.cache_clear()
 
     def assertFileFound(self, filename):
+        # Some temp directories are symlinks. Python resolves these fully while
+        # importing.
+        resolved_filename = filename.resolve()
         self.clear_autoreload_caches()
         # Test uncached access
-        self.assertIn(filename, autoreload.gen_filenames())
+        self.assertIn(resolved_filename, list(autoreload.iter_all_python_module_files()))
         # Test cached access
-        self.assertIn(filename, autoreload.gen_filenames())
+        self.assertIn(resolved_filename, list(autoreload.iter_all_python_module_files()))
+        self.assertEqual(autoreload.iter_modules_and_files.cache_info().hits, 1)
 
     def assertFileNotFound(self, filename):
+        resolved_filename = filename.resolve()
         self.clear_autoreload_caches()
         # Test uncached access
-        self.assertNotIn(filename, autoreload.gen_filenames())
-        # Test cached access
-        self.assertNotIn(filename, autoreload.gen_filenames())
-
-    def assertFileFoundOnlyNew(self, filename):
-        self.clear_autoreload_caches()
-        # Test uncached access
-        self.assertIn(filename, autoreload.gen_filenames(only_new=True))
+        self.assertNotIn(resolved_filename, list(autoreload.iter_all_python_module_files()))
         # Test cached access
-        self.assertNotIn(filename, autoreload.gen_filenames(only_new=True))
-
-    def test_django_locales(self):
-        """
-        gen_filenames() yields the built-in Django locale files.
-        """
-        django_dir = os.path.join(os.path.dirname(conf.__file__), 'locale')
-        django_mo = os.path.join(django_dir, 'nl', 'LC_MESSAGES', 'django.mo')
-        self.assertFileFound(django_mo)
-
-    @override_settings(LOCALE_PATHS=[LOCALE_PATH])
-    def test_locale_paths_setting(self):
-        """
-        gen_filenames also yields from LOCALE_PATHS locales.
-        """
-        locale_paths_mo = os.path.join(LOCALE_PATH, 'nl', 'LC_MESSAGES', 'django.mo')
-        self.assertFileFound(locale_paths_mo)
-
-    @override_settings(INSTALLED_APPS=[])
-    def test_project_root_locale(self):
-        """
-        gen_filenames() also yields from the current directory (project root).
-        """
-        old_cwd = os.getcwd()
-        os.chdir(os.path.dirname(__file__))
-        current_dir = os.path.join(os.path.dirname(__file__), 'locale')
-        current_dir_mo = os.path.join(current_dir, 'nl', 'LC_MESSAGES', 'django.mo')
-        try:
-            self.assertFileFound(current_dir_mo)
-        finally:
-            os.chdir(old_cwd)
-
-    @override_settings(INSTALLED_APPS=['django.contrib.admin'])
-    def test_app_locales(self):
-        """
-        gen_filenames() also yields from locale dirs in installed apps.
-        """
-        admin_dir = os.path.join(os.path.dirname(admin.__file__), 'locale')
-        admin_mo = os.path.join(admin_dir, 'nl', 'LC_MESSAGES', 'django.mo')
-        self.assertFileFound(admin_mo)
+        self.assertNotIn(resolved_filename, list(autoreload.iter_all_python_module_files()))
+        self.assertEqual(autoreload.iter_modules_and_files.cache_info().hits, 1)
 
-    @override_settings(USE_I18N=False)
-    def test_no_i18n(self):
-        """
-        If i18n machinery is disabled, there is no need for watching the
-        locale files.
-        """
-        django_dir = os.path.join(os.path.dirname(conf.__file__), 'locale')
-        django_mo = os.path.join(django_dir, 'nl', 'LC_MESSAGES', 'django.mo')
-        self.assertFileNotFound(django_mo)
-
-    def test_paths_are_native_strings(self):
-        for filename in autoreload.gen_filenames():
-            self.assertIsInstance(filename, str)
-
-    def test_only_new_files(self):
-        """
-        When calling a second time gen_filenames with only_new = True, only
-        files from newly loaded modules should be given.
-        """
+    def temporary_file(self, filename):
         dirname = tempfile.mkdtemp()
-        filename = os.path.join(dirname, 'test_only_new_module.py')
         self.addCleanup(shutil.rmtree, dirname)
-        with open(filename, 'w'):
-            pass
-
-        # Test uncached access
-        self.clear_autoreload_caches()
-        filenames = set(autoreload.gen_filenames(only_new=True))
-        filenames_reference = set(autoreload.gen_filenames())
-        self.assertEqual(filenames, filenames_reference)
-
-        # Test cached access: no changes
-        filenames = set(autoreload.gen_filenames(only_new=True))
-        self.assertEqual(filenames, set())
+        return Path(dirname) / filename
 
-        # Test cached access: add a module
-        with extend_sys_path(dirname):
-            import_module('test_only_new_module')
-        filenames = set(autoreload.gen_filenames(only_new=True))
-        self.assertEqual(filenames, {filename})
+    def test_paths_are_pathlib_instances(self):
+        for filename in autoreload.iter_all_python_module_files():
+            self.assertIsInstance(filename, Path)
 
-    def test_deleted_removed(self):
+    def test_file_added(self):
         """
-        When a file is deleted, gen_filenames() no longer returns it.
+        When a file is added, it's returned by iter_all_python_module_files().
         """
-        dirname = tempfile.mkdtemp()
-        filename = os.path.join(dirname, 'test_deleted_removed_module.py')
-        self.addCleanup(shutil.rmtree, dirname)
-        with open(filename, 'w'):
-            pass
+        filename = self.temporary_file('test_deleted_removed_module.py')
+        filename.touch()
 
-        with extend_sys_path(dirname):
-            import_module('test_deleted_removed_module')
-        self.assertFileFound(filename)
+        with extend_sys_path(str(filename.parent)):
+            self.import_and_cleanup('test_deleted_removed_module')
 
-        os.unlink(filename)
-        self.assertFileNotFound(filename)
+        self.assertFileFound(filename.absolute())
 
     def test_check_errors(self):
         """
         When a file containing an error is imported in a function wrapped by
         check_errors(), gen_filenames() returns it.
         """
-        dirname = tempfile.mkdtemp()
-        filename = os.path.join(dirname, 'test_syntax_error.py')
-        self.addCleanup(shutil.rmtree, dirname)
-        with open(filename, 'w') as f:
-            f.write("Ceci n'est pas du Python.")
+        filename = self.temporary_file('test_syntax_error.py')
+        filename.write_text("Ceci n'est pas du Python.")
 
-        with extend_sys_path(dirname):
+        with extend_sys_path(str(filename.parent)):
             with self.assertRaises(SyntaxError):
                 autoreload.check_errors(import_module)('test_syntax_error')
         self.assertFileFound(filename)
 
-    def test_check_errors_only_new(self):
-        """
-        When a file containing an error is imported in a function wrapped by
-        check_errors(), gen_filenames(only_new=True) returns it.
-        """
-        dirname = tempfile.mkdtemp()
-        filename = os.path.join(dirname, 'test_syntax_error.py')
-        self.addCleanup(shutil.rmtree, dirname)
-        with open(filename, 'w') as f:
-            f.write("Ceci n'est pas du Python.")
-
-        with extend_sys_path(dirname):
-            with self.assertRaises(SyntaxError):
-                autoreload.check_errors(import_module)('test_syntax_error')
-        self.assertFileFoundOnlyNew(filename)
-
     def test_check_errors_catches_all_exceptions(self):
         """
         Since Python may raise arbitrary exceptions when importing code,
         check_errors() must catch Exception, not just some subclasses.
         """
-        dirname = tempfile.mkdtemp()
-        filename = os.path.join(dirname, 'test_exception.py')
-        self.addCleanup(shutil.rmtree, dirname)
-        with open(filename, 'w') as f:
-            f.write("raise Exception")
-
-        with extend_sys_path(dirname):
+        filename = self.temporary_file('test_exception.py')
+        filename.write_text('raise Exception')
+        with extend_sys_path(str(filename.parent)):
             with self.assertRaises(Exception):
                 autoreload.check_errors(import_module)('test_exception')
         self.assertFileFound(filename)
 
-
-class CleanFilesTests(SimpleTestCase):
-    TEST_MAP = {
-        # description: (input_file_list, expected_returned_file_list)
-        'falsies': ([None, False], []),
-        'pycs': (['myfile.pyc'], ['myfile.py']),
-        'pyos': (['myfile.pyo'], ['myfile.py']),
-        '$py.class': (['myclass$py.class'], ['myclass.py']),
-        'combined': (
-            [None, 'file1.pyo', 'file2.pyc', 'myclass$py.class'],
-            ['file1.py', 'file2.py', 'myclass.py'],
-        )
-    }
-
-    def _run_tests(self, mock_files_exist=True):
-        with mock.patch('django.utils.autoreload.os.path.exists', return_value=mock_files_exist):
-            for description, values in self.TEST_MAP.items():
-                filenames, expected_returned_filenames = values
-                self.assertEqual(
-                    autoreload.clean_files(filenames),
-                    expected_returned_filenames if mock_files_exist else [],
-                    msg='{} failed for input file list: {}; returned file list: {}'.format(
-                        description, filenames, expected_returned_filenames
-                    ),
-                )
-
-    def test_files_exist(self):
+    def test_zip_reload(self):
         """
-        If the file exists, any compiled files (pyc, pyo, $py.class) are
-        transformed as their source files.
+        Modules imported from zipped files have their archive location included
+        in the result.
         """
-        self._run_tests()
+        zip_file = self.temporary_file('zip_import.zip')
+        with zipfile.ZipFile(str(zip_file), 'w', zipfile.ZIP_DEFLATED) as zipf:
+            zipf.writestr('test_zipped_file.py', '')
 
-    def test_files_do_not_exist(self):
-        """
-        If the files don't exist, they aren't in the returned file list.
-        """
-        self._run_tests(mock_files_exist=False)
+        with extend_sys_path(str(zip_file)):
+            self.import_and_cleanup('test_zipped_file')
+        self.assertFileFound(zip_file)
 
+    def test_bytecode_conversion_to_source(self):
+        """.pyc and .pyo files are included in the files list."""
+        filename = self.temporary_file('test_compiled.py')
+        filename.touch()
+        compiled_file = Path(py_compile.compile(str(filename), str(filename.with_suffix('.pyc'))))
+        filename.unlink()
+        with extend_sys_path(str(compiled_file.parent)):
+            self.import_and_cleanup('test_compiled')
+        self.assertFileFound(compiled_file)
 
-class ResetTranslationsTests(SimpleTestCase):
 
+class TestCommonRoots(SimpleTestCase):
+    def test_common_roots(self):
+        paths = (
+            Path('/first/second'),
+            Path('/first/second/third'),
+            Path('/first/'),
+            Path('/root/first/'),
+        )
+        results = autoreload.common_roots(paths)
+        self.assertCountEqual(results, [Path('/first/'), Path('/root/first/')])
+
+
+class TestSysPathDirectories(SimpleTestCase):
     def setUp(self):
-        self.gettext_translations = gettext._translations.copy()
-        self.trans_real_translations = trans_real._translations.copy()
+        self._directory = tempfile.TemporaryDirectory()
+        self.directory = Path(self._directory.name).resolve().absolute()
+        self.file = self.directory / 'test'
+        self.file.touch()
 
     def tearDown(self):
-        gettext._translations = self.gettext_translations
-        trans_real._translations = self.trans_real_translations
+        self._directory.cleanup()
+
+    def test_sys_paths_with_directories(self):
+        with extend_sys_path(str(self.file)):
+            paths = list(autoreload.sys_path_directories())
+        self.assertIn(self.file.parent, paths)
+
+    def test_sys_paths_non_existing(self):
+        nonexistant_file = Path(self.directory.name) / 'does_not_exist'
+        with extend_sys_path(str(nonexistant_file)):
+            paths = list(autoreload.sys_path_directories())
+        self.assertNotIn(nonexistant_file, paths)
+        self.assertNotIn(nonexistant_file.parent, paths)
+
+    def test_sys_paths_absolute(self):
+        paths = list(autoreload.sys_path_directories())
+        self.assertTrue(all(p.is_absolute() for p in paths))
+
+    def test_sys_paths_directories(self):
+        with extend_sys_path(str(self.directory)):
+            paths = list(autoreload.sys_path_directories())
+        self.assertIn(self.directory, paths)
+
+
+class GetReloaderTests(SimpleTestCase):
+    @mock.patch('django.utils.autoreload.WatchmanReloader')
+    def test_watchman_unavailable(self, mocked_watchman):
+        mocked_watchman.check_availability.side_effect = WatchmanUnavailable
+        self.assertIsInstance(autoreload.get_reloader(), autoreload.StatReloader)
+
+    @mock.patch.object(autoreload.WatchmanReloader, 'check_availability')
+    def test_watchman_available(self, mocked_available):
+        # If WatchmanUnavailable isn't raised, Watchman will be chosen.
+        mocked_available.return_value = None
+        result = autoreload.get_reloader()
+        self.assertIsInstance(result, autoreload.WatchmanReloader)
+
 
-    def test_resets_gettext(self):
-        gettext._translations = {'foo': 'bar'}
-        autoreload.reset_translations()
-        self.assertEqual(gettext._translations, {})
+class RunWithReloaderTests(SimpleTestCase):
+    @mock.patch.dict(os.environ, {autoreload.DJANGO_AUTORELOAD_ENV: 'true'})
+    @mock.patch('django.utils.autoreload.get_reloader')
+    def test_swallows_keyboard_interrupt(self, mocked_get_reloader):
+        mocked_get_reloader.side_effect = KeyboardInterrupt()
+        autoreload.run_with_reloader(lambda: None)  # No exception
 
-    def test_resets_trans_real(self):
-        trans_real._translations = {'foo': 'bar'}
-        trans_real._default = 1
-        trans_real._active = False
-        autoreload.reset_translations()
-        self.assertEqual(trans_real._translations, {})
-        self.assertIsNone(trans_real._default)
-        self.assertIsInstance(trans_real._active, _thread._local)
+    @mock.patch.dict(os.environ, {autoreload.DJANGO_AUTORELOAD_ENV: 'false'})
+    @mock.patch('django.utils.autoreload.restart_with_reloader')
+    def test_calls_sys_exit(self, mocked_restart_reloader):
+        mocked_restart_reloader.return_value = 1
+        with self.assertRaises(SystemExit) as exc:
+            autoreload.run_with_reloader(lambda: None)
+        self.assertEqual(exc.exception.code, 1)
+
+    @mock.patch.dict(os.environ, {autoreload.DJANGO_AUTORELOAD_ENV: 'true'})
+    @mock.patch('django.utils.autoreload.start_django')
+    @mock.patch('django.utils.autoreload.get_reloader')
+    def test_calls_start_django(self, mocked_reloader, mocked_start_django):
+        mocked_reloader.return_value = mock.sentinel.RELOADER
+        autoreload.run_with_reloader(mock.sentinel.METHOD)
+        self.assertEqual(mocked_start_django.call_count, 1)
+        self.assertSequenceEqual(
+            mocked_start_django.call_args[0],
+            [mock.sentinel.RELOADER, mock.sentinel.METHOD]
+        )
+
+
+class StartDjangoTests(SimpleTestCase):
+    @mock.patch('django.utils.autoreload.StatReloader')
+    def test_watchman_becomes_unavailable(self, mocked_stat):
+        mocked_stat.should_stop.return_value = True
+        fake_reloader = mock.MagicMock()
+        fake_reloader.should_stop = False
+        fake_reloader.run.side_effect = autoreload.WatchmanUnavailable()
+
+        autoreload.start_django(fake_reloader, lambda: None)
+        self.assertEqual(mocked_stat.call_count, 1)
+
+    @mock.patch('django.utils.autoreload.ensure_echo_on')
+    def test_echo_on_called(self, mocked_echo):
+        fake_reloader = mock.MagicMock()
+        autoreload.start_django(fake_reloader, lambda: None)
+        self.assertEqual(mocked_echo.call_count, 1)
+
+    @mock.patch('django.utils.autoreload.check_errors')
+    def test_check_errors_called(self, mocked_check_errors):
+        fake_method = mock.MagicMock(return_value=None)
+        fake_reloader = mock.MagicMock()
+        autoreload.start_django(fake_reloader, fake_method)
+        self.assertCountEqual(mocked_check_errors.call_args[0], [fake_method])
+
+    @mock.patch('threading.Thread')
+    @mock.patch('django.utils.autoreload.check_errors')
+    def test_starts_thread_with_args(self, mocked_check_errors, mocked_thread):
+        fake_reloader = mock.MagicMock()
+        fake_main_func = mock.MagicMock()
+        fake_thread = mock.MagicMock()
+        mocked_check_errors.return_value = fake_main_func
+        mocked_thread.return_value = fake_thread
+        autoreload.start_django(fake_reloader, fake_main_func, 123, abc=123)
+        self.assertEqual(mocked_thread.call_count, 1)
+        self.assertEqual(
+            mocked_thread.call_args[1],
+            {'target': fake_main_func, 'args': (123,), 'kwargs': {'abc': 123}}
+        )
+        self.assertSequenceEqual(fake_thread.setDaemon.call_args[0], [True])
+        self.assertTrue(fake_thread.start.called)
+
+
+class TestCheckErrors(SimpleTestCase):
+    def test_mutates_error_files(self):
+        fake_method = mock.MagicMock(side_effect=RuntimeError())
+        wrapped = autoreload.check_errors(fake_method)
+        with mock.patch.object(autoreload, '_error_files') as mocked_error_files:
+            with self.assertRaises(RuntimeError):
+                wrapped()
+        self.assertEqual(mocked_error_files.append.call_count, 1)
+
+
+class TestRaiseLastException(SimpleTestCase):
+    @mock.patch('django.utils.autoreload._exception', None)
+    def test_no_exception(self):
+        # Should raise no exception if _exception is None
+        autoreload.raise_last_exception()
+
+    def test_raises_exception(self):
+        class MyException(Exception):
+            pass
+
+        # Create an exception
+        try:
+            raise MyException('Test Message')
+        except MyException:
+            exc_info = sys.exc_info()
+
+        with mock.patch('django.utils.autoreload._exception', exc_info):
+            with self.assertRaises(MyException, msg='Test Message'):
+                autoreload.raise_last_exception()
 
 
 class RestartWithReloaderTests(SimpleTestCase):
@@ -286,3 +308,363 @@ class RestartWithReloaderTests(SimpleTestCase):
             autoreload.restart_with_reloader()
             self.assertEqual(mock_call.call_count, 1)
             self.assertEqual(mock_call.call_args[0][0], [self.executable, '-Wall', '-m', 'django'] + argv[1:])
+
+
+class ReloaderTests(SimpleTestCase):
+    RELOADER_CLS = None
+
+    def setUp(self):
+        self._tempdir = tempfile.TemporaryDirectory()
+        self.tempdir = Path(self._tempdir.name).resolve().absolute()
+        self.existing_file = self.ensure_file(self.tempdir / 'test.py')
+        self.nonexistant_file = (self.tempdir / 'does_not_exist.py').absolute()
+        self.reloader = self.RELOADER_CLS()
+
+    def tearDown(self):
+        self._tempdir.cleanup()
+        self.reloader.stop()
+
+    def ensure_file(self, path):
+        path.parent.mkdir(exist_ok=True, parents=True)
+        path.touch()
+        # On Linux and Windows updating the mtime of a file using touch() will set a timestamp
+        # value that is in the past, as the time value for the last kernel tick is used rather
+        # than getting the correct absolute time.
+        # To make testing simpler set the mtime to be the observed time when this function is
+        # called.
+        self.set_mtime(path, time.time())
+        return path.absolute()
+
+    def set_mtime(self, fp, value):
+        os.utime(str(fp), (value, value))
+
+    def increment_mtime(self, fp, by=1):
+        current_time = time.time()
+        self.set_mtime(fp, current_time + by)
+
+    @contextlib.contextmanager
+    def tick_twice(self):
+        ticker = self.reloader.tick()
+        next(ticker)
+        yield
+        next(ticker)
+
+
+class IntegrationTests:
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_file(self, mocked_modules, notify_mock):
+        self.reloader.watch_file(self.existing_file)
+        with self.tick_twice():
+            self.increment_mtime(self.existing_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [self.existing_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_nonexistant_file(self, mocked_modules, notify_mock):
+        self.reloader.watch_file(self.nonexistant_file)
+        with self.tick_twice():
+            self.ensure_file(self.nonexistant_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [self.nonexistant_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_nonexistant_file_in_non_existing_directory(self, mocked_modules, notify_mock):
+        non_existing_directory = self.tempdir / 'non_existing_dir'
+        nonexistant_file = non_existing_directory / 'test'
+        self.reloader.watch_file(nonexistant_file)
+        with self.tick_twice():
+            self.ensure_file(nonexistant_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [nonexistant_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_glob(self, mocked_modules, notify_mock):
+        non_py_file = self.ensure_file(self.tempdir / 'non_py_file')
+        self.reloader.watch_dir(self.tempdir, '*.py')
+        with self.tick_twice():
+            self.increment_mtime(non_py_file)
+            self.increment_mtime(self.existing_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [self.existing_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_glob_non_existing_directory(self, mocked_modules, notify_mock):
+        non_existing_directory = self.tempdir / 'does_not_exist'
+        nonexistant_file = non_existing_directory / 'test.py'
+        self.reloader.watch_dir(non_existing_directory, '*.py')
+        with self.tick_twice():
+            self.ensure_file(nonexistant_file)
+            self.set_mtime(nonexistant_file, time.time())
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [nonexistant_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_multiple_globs(self, mocked_modules, notify_mock):
+        self.ensure_file(self.tempdir / 'x.test')
+        self.reloader.watch_dir(self.tempdir, '*.py')
+        self.reloader.watch_dir(self.tempdir, '*.test')
+        with self.tick_twice():
+            self.increment_mtime(self.existing_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [self.existing_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_overlapping_globs(self, mocked_modules, notify_mock):
+        self.reloader.watch_dir(self.tempdir, '*.py')
+        self.reloader.watch_dir(self.tempdir, '*.p*')
+        with self.tick_twice():
+            self.increment_mtime(self.existing_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [self.existing_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_glob_recursive(self, mocked_modules, notify_mock):
+        non_py_file = self.ensure_file(self.tempdir / 'dir' / 'non_py_file')
+        py_file = self.ensure_file(self.tempdir / 'dir' / 'file.py')
+        self.reloader.watch_dir(self.tempdir, '**/*.py')
+        with self.tick_twice():
+            self.increment_mtime(non_py_file)
+            self.increment_mtime(py_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [py_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_multiple_recursive_globs(self, mocked_modules, notify_mock):
+        non_py_file = self.ensure_file(self.tempdir / 'dir' / 'test.txt')
+        py_file = self.ensure_file(self.tempdir / 'dir' / 'file.py')
+        self.reloader.watch_dir(self.tempdir, '**/*.txt')
+        self.reloader.watch_dir(self.tempdir, '**/*.py')
+        with self.tick_twice():
+            self.increment_mtime(non_py_file)
+            self.increment_mtime(py_file)
+        self.assertEqual(notify_mock.call_count, 2)
+        self.assertCountEqual(notify_mock.call_args_list, [mock.call(py_file), mock.call(non_py_file)])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_nested_glob_recursive(self, mocked_modules, notify_mock):
+        inner_py_file = self.ensure_file(self.tempdir / 'dir' / 'file.py')
+        self.reloader.watch_dir(self.tempdir, '**/*.py')
+        self.reloader.watch_dir(inner_py_file.parent, '**/*.py')
+        with self.tick_twice():
+            self.increment_mtime(inner_py_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [inner_py_file])
+
+    @mock.patch('django.utils.autoreload.BaseReloader.notify_file_changed')
+    @mock.patch('django.utils.autoreload.iter_all_python_module_files', return_value=frozenset())
+    def test_overlapping_glob_recursive(self, mocked_modules, notify_mock):
+        py_file = self.ensure_file(self.tempdir / 'dir' / 'file.py')
+        self.reloader.watch_dir(self.tempdir, '**/*.p*')
+        self.reloader.watch_dir(self.tempdir, '**/*.py*')
+        with self.tick_twice():
+            self.increment_mtime(py_file)
+        self.assertEqual(notify_mock.call_count, 1)
+        self.assertCountEqual(notify_mock.call_args[0], [py_file])
+
+
+class BaseReloaderTests(ReloaderTests):
+    RELOADER_CLS = autoreload.BaseReloader
+
+    def test_watch_without_absolute(self):
+        with self.assertRaisesMessage(ValueError, 'test.py must be absolute.'):
+            self.reloader.watch_file('test.py')
+
+    def test_watch_with_single_file(self):
+        self.reloader.watch_file(self.existing_file)
+        watched_files = list(self.reloader.watched_files())
+        self.assertIn(self.existing_file, watched_files)
+
+    def test_watch_with_glob(self):
+        self.reloader.watch_dir(self.tempdir, '*.py')
+        watched_files = list(self.reloader.watched_files())
+        self.assertIn(self.existing_file, watched_files)
+
+    def test_watch_files_with_recursive_glob(self):
+        inner_file = self.ensure_file(self.tempdir / 'test' / 'test.py')
+        self.reloader.watch_dir(self.tempdir, '**/*.py')
+        watched_files = list(self.reloader.watched_files())
+        self.assertIn(self.existing_file, watched_files)
+        self.assertIn(inner_file, watched_files)
+
+    def test_run_loop_catches_stopiteration(self):
+        def mocked_tick():
+            yield
+
+        with mock.patch.object(self.reloader, 'tick', side_effect=mocked_tick) as tick:
+            self.reloader.run_loop()
+        self.assertEqual(tick.call_count, 1)
+
+    def test_run_loop_stop_and_return(self):
+        def mocked_tick(*args):
+            yield
+            self.reloader.stop()
+            return  # Raises StopIteration
+
+        with mock.patch.object(self.reloader, 'tick', side_effect=mocked_tick) as tick:
+            self.reloader.run_loop()
+
+        self.assertEqual(tick.call_count, 1)
+
+    def test_wait_for_apps_ready_checks_for_exception(self):
+        app_reg = Apps()
+        app_reg.ready_event.set()
+        # thread.is_alive() is False if it's not started.
+        dead_thread = threading.Thread()
+        self.assertFalse(self.reloader.wait_for_apps_ready(app_reg, dead_thread))
+
+    def test_wait_for_apps_ready_without_exception(self):
+        app_reg = Apps()
+        app_reg.ready_event.set()
+        thread = mock.MagicMock()
+        thread.is_alive.return_value = True
+        self.assertTrue(self.reloader.wait_for_apps_ready(app_reg, thread))
+
+
+def skip_unless_watchman_available():
+    try:
+        autoreload.WatchmanReloader.check_availability()
+    except WatchmanUnavailable as e:
+        return skip('Watchman unavailable: %s' % e)
+    return lambda func: func
+
+
+@skip_unless_watchman_available()
+class WatchmanReloaderTests(ReloaderTests, IntegrationTests):
+    RELOADER_CLS = autoreload.WatchmanReloader
+
+    def test_watch_glob_ignores_non_existing_directories_two_levels(self):
+        with mock.patch.object(self.reloader, '_subscribe') as mocked_subscribe:
+            self.reloader._watch_glob(self.tempdir / 'does_not_exist' / 'more', ['*'])
+        self.assertFalse(mocked_subscribe.called)
+
+    def test_watch_glob_uses_existing_parent_directories(self):
+        with mock.patch.object(self.reloader, '_subscribe') as mocked_subscribe:
+            self.reloader._watch_glob(self.tempdir / 'does_not_exist', ['*'])
+        self.assertSequenceEqual(
+            mocked_subscribe.call_args[0],
+            [
+                self.tempdir, 'glob-parent-does_not_exist:%s' % self.tempdir,
+                ['anyof', ['match', 'does_not_exist/*', 'wholename']]
+            ]
+        )
+
+    def test_watch_glob_multiple_patterns(self):
+        with mock.patch.object(self.reloader, '_subscribe') as mocked_subscribe:
+            self.reloader._watch_glob(self.tempdir, ['*', '*.py'])
+        self.assertSequenceEqual(
+            mocked_subscribe.call_args[0],
+            [
+                self.tempdir, 'glob:%s' % self.tempdir,
+                ['anyof', ['match', '*', 'wholename'], ['match', '*.py', 'wholename']]
+            ]
+        )
+
+    def test_watched_roots_contains_files(self):
+        paths = self.reloader.watched_roots([self.existing_file])
+        self.assertIn(self.existing_file.parent, paths)
+
+    def test_watched_roots_contains_directory_globs(self):
+        self.reloader.watch_dir(self.tempdir, '*.py')
+        paths = self.reloader.watched_roots([])
+        self.assertIn(self.tempdir, paths)
+
+    def test_watched_roots_contains_sys_path(self):
+        with extend_sys_path(str(self.tempdir)):
+            paths = self.reloader.watched_roots([])
+        self.assertIn(self.tempdir, paths)
+
+    def test_check_server_status(self):
+        self.assertTrue(self.reloader.check_server_status())
+
+    def test_check_server_status_raises_error(self):
+        with mock.patch.object(self.reloader.client, 'query') as mocked_query:
+            mocked_query.side_effect = Exception()
+            with self.assertRaises(autoreload.WatchmanUnavailable):
+                self.reloader.check_server_status()
+
+    @mock.patch('pywatchman.client')
+    def test_check_availability(self, mocked_client):
+        mocked_client().capabilityCheck.side_effect = Exception()
+        with self.assertRaisesMessage(WatchmanUnavailable, 'Cannot connect to the watchman service'):
+            self.RELOADER_CLS.check_availability()
+
+    @mock.patch('pywatchman.client')
+    def test_check_availability_lower_version(self, mocked_client):
+        mocked_client().capabilityCheck.return_value = {'version': '4.8.10'}
+        with self.assertRaisesMessage(WatchmanUnavailable, 'Watchman 4.9 or later is required.'):
+            self.RELOADER_CLS.check_availability()
+
+    def test_pywatchman_not_available(self):
+        with mock.patch.object(autoreload, 'pywatchman') as mocked:
+            mocked.__bool__.return_value = False
+            with self.assertRaisesMessage(WatchmanUnavailable, 'pywatchman not installed.'):
+                self.RELOADER_CLS.check_availability()
+
+    def test_update_watches_raises_exceptions(self):
+        class TestException(Exception):
+            pass
+
+        with mock.patch.object(self.reloader, '_update_watches') as mocked_watches:
+            with mock.patch.object(self.reloader, 'check_server_status') as mocked_server_status:
+                mocked_watches.side_effect = TestException()
+                mocked_server_status.return_value = True
+                with self.assertRaises(TestException):
+                    self.reloader.update_watches()
+                self.assertIsInstance(mocked_server_status.call_args[0][0], TestException)
+
+
+class StatReloaderTests(ReloaderTests, IntegrationTests):
+    RELOADER_CLS = autoreload.StatReloader
+
+    def setUp(self):
+        super().setUp()
+        # Shorten the sleep time to speed up tests.
+        self.reloader.SLEEP_TIME = 0.01
+
+    def test_snapshot_files_ignores_missing_files(self):
+        with mock.patch.object(self.reloader, 'watched_files', return_value=[self.nonexistant_file]):
+            self.assertEqual(dict(self.reloader.snapshot_files()), {})
+
+    def test_snapshot_files_updates(self):
+        with mock.patch.object(self.reloader, 'watched_files', return_value=[self.existing_file]):
+            snapshot1 = dict(self.reloader.snapshot_files())
+            self.assertIn(self.existing_file, snapshot1)
+            self.increment_mtime(self.existing_file)
+            snapshot2 = dict(self.reloader.snapshot_files())
+            self.assertNotEqual(snapshot1[self.existing_file], snapshot2[self.existing_file])
+
+    def test_does_not_fire_without_changes(self):
+        with mock.patch.object(self.reloader, 'watched_files', return_value=[self.existing_file]), \
+                mock.patch.object(self.reloader, 'notify_file_changed') as notifier:
+            mtime = self.existing_file.stat().st_mtime
+            initial_snapshot = {self.existing_file: mtime}
+            second_snapshot = self.reloader.loop_files(initial_snapshot, time.time())
+            self.assertEqual(second_snapshot, {})
+            notifier.assert_not_called()
+
+    def test_fires_when_created(self):
+        with mock.patch.object(self.reloader, 'watched_files', return_value=[self.nonexistant_file]), \
+                mock.patch.object(self.reloader, 'notify_file_changed') as notifier:
+            self.nonexistant_file.touch()
+            mtime = self.nonexistant_file.stat().st_mtime
+            second_snapshot = self.reloader.loop_files({}, mtime - 1)
+            self.assertCountEqual(second_snapshot.keys(), [self.nonexistant_file])
+            notifier.assert_called_once_with(self.nonexistant_file)
+
+    def test_fires_with_changes(self):
+        with mock.patch.object(self.reloader, 'watched_files', return_value=[self.existing_file]), \
+                mock.patch.object(self.reloader, 'notify_file_changed') as notifier:
+            initial_snapshot = {self.existing_file: 1}
+            second_snapshot = self.reloader.loop_files(initial_snapshot, time.time())
+            notifier.assert_called_once_with(self.existing_file)
+            self.assertCountEqual(second_snapshot.keys(), [self.existing_file])