gh-80958: Restore unittest discovery support for namespace packages as start directory

Doc/library/unittest.rst

@@ -272,7 +272,8 @@ Test Discovery
 
 Unittest supports simple test discovery. In order to be compatible with test
 discovery, all of the test files must be :ref:`modules <tut-modules>` or
-:ref:`packages <tut-packages>` importable from the top-level directory of
+:ref:`packages <tut-packages>` (including :term:`namespace packages
+<namespace package>`) importable from the top-level directory of
 the project (this means that their filenames must be valid :ref:`identifiers
 <identifiers>`).
 
@@ -345,24 +346,6 @@ the `load_tests protocol`_.
    directory too (e.g.
    ``python -m unittest discover -s root/namespace -t root``).
 
-.. versionchanged:: 3.11
-   :mod:`unittest` dropped the :term:`namespace packages <namespace package>`
-   support in Python 3.11. It has been broken since Python 3.7. Start directory and
-   subdirectories containing tests must be regular package that have
-   ``__init__.py`` file.
-
-   Directories containing start directory still can be a namespace package.
-   In this case, you need to specify start directory as dotted package name,
-   and target directory explicitly. For example::
-
-      # proj/  <-- current directory
-      #   namespace/
-      #     mypkg/
-      #       __init__.py
-      #       test_mypkg.py
-
-      python -m unittest discover -s namespace.mypkg -t .
-
 
 .. _organizing-tests:
 
@@ -1928,10 +1911,6 @@ Loading and running tests
          whether their path matches *pattern*, because it is impossible for
          a package name to match the default pattern.
 
-      .. versionchanged:: 3.11
-         *start_dir* can not be a :term:`namespace packages <namespace package>`.
-         It has been broken since Python 3.7 and Python 3.11 officially remove it.
-
       .. versionchanged:: 3.13
          *top_level_dir* is only stored for the duration of *discover* call.
 

Doc/whatsnew/3.11.rst

@@ -2028,10 +2028,6 @@ Removed C APIs are :ref:`listed separately <whatsnew311-c-api-removed>`.
 * Removed the deprecated :meth:`!split` method of :class:`!_tkinter.TkappType`.
   (Contributed by Erlend E. Aasland in :issue:`38371`.)
 
-* Removed namespace package support from :mod:`unittest` discovery.
-  It was introduced in Python 3.4 but has been broken since Python 3.7.
-  (Contributed by Inada Naoki in :issue:`23882`.)
-
 * Removed the undocumented private :meth:`!float.__set_format__` method,
   previously known as :meth:`!float.__setformat__` in Python 3.7.
   Its docstring said: "You probably don't want to use this function.

Lib/test/test_unittest/test_discovery.py

@@ -4,12 +4,14 @@
 import sys
 import types
 import pickle
+from importlib._bootstrap_external import NamespaceLoader
 from test import support
 from test.support import import_helper
 
 import unittest
 import unittest.mock
 import test.test_unittest
+from test.test_importlib import util as test_util
 
 
 class TestableTestProgram(unittest.TestProgram):
@@ -395,7 +397,7 @@ def restore_isdir():
         self.addCleanup(restore_isdir)
 
         _find_tests_args = []
-        def _find_tests(start_dir, pattern):
+        def _find_tests(start_dir, pattern, namespace=None):
             _find_tests_args.append((start_dir, pattern))
             return ['tests']
         loader._find_tests = _find_tests
@@ -815,7 +817,7 @@ def test_discovery_from_dotted_path(self):
         expectedPath = os.path.abspath(os.path.dirname(test.test_unittest.__file__))
 
         self.wasRun = False
-        def _find_tests(start_dir, pattern):
+        def _find_tests(start_dir, pattern, namespace=None):
             self.wasRun = True
             self.assertEqual(start_dir, expectedPath)
             return tests
@@ -848,6 +850,40 @@ def restore():
                          'Can not use builtin modules '
                          'as dotted module names')
 
+    def test_discovery_from_dotted_namespace_packages(self):
+        loader = unittest.TestLoader()
+
+        package = types.ModuleType('package')
+        package.__name__ = "tests"
+        package.__path__ = ['/a', '/b']
+        package.__file__ = None
+        package.__spec__ = types.SimpleNamespace(
+            name=package.__name__,
+            loader=NamespaceLoader(package.__name__, package.__path__, None),
+            submodule_search_locations=['/a', '/b']
+        )
+
+        def _import(packagename, *args, **kwargs):
+            sys.modules[packagename] = package
+            return package
+
+        _find_tests_args = []
+        def _find_tests(start_dir, pattern, namespace=None):
+            _find_tests_args.append((start_dir, pattern))
+            return ['%s/tests' % start_dir]
+
+        loader._find_tests = _find_tests
+        loader.suiteClass = list
+
+        with unittest.mock.patch('builtins.__import__', _import):
+            # Since loader.discover() can modify sys.path, restore it when done.
+            with import_helper.DirsOnSysPath():
+                # Make sure to remove 'package' from sys.modules when done.
+                with test_util.uncache('package'):
+                    suite = loader.discover('package')
+
+        self.assertEqual(suite, ['/a/tests', '/b/tests'])
+
     def test_discovery_failed_discovery(self):
         from test.test_importlib import util
 

Lib/unittest/loader.py

@@ -274,6 +274,8 @@ def discover(self, start_dir, pattern='test*.py', top_level_dir=None):
         self._top_level_dir = top_level_dir
 
         is_not_importable = False
+        is_namespace = False
+        tests = []
         if os.path.isdir(os.path.abspath(start_dir)):
             start_dir = os.path.abspath(start_dir)
             if start_dir != top_level_dir:
@@ -286,12 +288,25 @@ def discover(self, start_dir, pattern='test*.py', top_level_dir=None):
                 is_not_importable = True
             else:
                 the_module = sys.modules[start_dir]
-                top_part = start_dir.split('.')[0]
-                try:
-                    start_dir = os.path.abspath(
-                        os.path.dirname((the_module.__file__)))
-                except AttributeError:
-                    if the_module.__name__ in sys.builtin_module_names:
+                if not hasattr(the_module, "__file__") or the_module.__file__ is None:
+                    # look for namespace packages
+                    try:
+                        spec = the_module.__spec__
+                    except AttributeError:
+                        spec = None
+
+                    if spec and spec.submodule_search_locations is not None:
+                        is_namespace = True
+
+                        for path in the_module.__path__:
+                            if (not set_implicit_top and
+                                not path.startswith(top_level_dir)):
+                                continue
+                            self._top_level_dir = \
+                                (path.split(the_module.__name__
+                                        .replace(".", os.path.sep))[0])
+                            tests.extend(self._find_tests(path, pattern, namespace=True))
+                    elif the_module.__name__ in sys.builtin_module_names:
                         # builtin module
                         raise TypeError('Can not use builtin modules '
                                         'as dotted module names') from None
@@ -300,14 +315,22 @@ def discover(self, start_dir, pattern='test*.py', top_level_dir=None):
                             f"don't know how to discover from {the_module!r}"
                             ) from None
 
+                else:
+                    top_part = start_dir.split('.')[0]
+                    start_dir = os.path.abspath(os.path.dirname((the_module.__file__)))
+
                 if set_implicit_top:
-                    self._top_level_dir = self._get_directory_containing_module(top_part)
+                    if not is_namespace:
+                        self._top_level_dir = \
+                           self._get_directory_containing_module(top_part)
                     sys.path.remove(top_level_dir)
 
         if is_not_importable:
             raise ImportError('Start directory is not importable: %r' % start_dir)
 
-        tests = list(self._find_tests(start_dir, pattern))
+        if not is_namespace:
+            tests = list(self._find_tests(start_dir, pattern))
+
         self._top_level_dir = original_top_level_dir
         return self.suiteClass(tests)
 
@@ -343,7 +366,7 @@ def _match_path(self, path, full_path, pattern):
         # override this method to use alternative matching strategy
         return fnmatch(path, pattern)
 
-    def _find_tests(self, start_dir, pattern):
+    def _find_tests(self, start_dir, pattern, namespace=False):
         """Used by discovery. Yields test suites it loads."""
         # Handle the __init__ in this package
         name = self._get_name_from_path(start_dir)
@@ -352,7 +375,8 @@ def _find_tests(self, start_dir, pattern):
         if name != '.' and name not in self._loading_packages:
             # name is in self._loading_packages while we have called into
             # loadTestsFromModule with name.
-            tests, should_recurse = self._find_test_path(start_dir, pattern)
+            tests, should_recurse = self._find_test_path(
+                start_dir, pattern, namespace)
             if tests is not None:
                 yield tests
             if not should_recurse:
@@ -363,19 +387,20 @@ def _find_tests(self, start_dir, pattern):
         paths = sorted(os.listdir(start_dir))
         for path in paths:
             full_path = os.path.join(start_dir, path)
-            tests, should_recurse = self._find_test_path(full_path, pattern)
+            tests, should_recurse = self._find_test_path(
+                full_path, pattern, namespace)
             if tests is not None:
                 yield tests
             if should_recurse:
                 # we found a package that didn't use load_tests.
                 name = self._get_name_from_path(full_path)
                 self._loading_packages.add(name)
                 try:
-                    yield from self._find_tests(full_path, pattern)
+                    yield from self._find_tests(full_path, pattern, namespace)
                 finally:
                     self._loading_packages.discard(name)
 
-    def _find_test_path(self, full_path, pattern):
+    def _find_test_path(self, full_path, pattern, namespace=False):
         """Used by discovery.
 
         Loads tests from a single file, or a directories' __init__.py when
@@ -419,7 +444,8 @@ def _find_test_path(self, full_path, pattern):
                         msg % (mod_name, module_dir, expected_dir))
                 return self.loadTestsFromModule(module, pattern=pattern), False
         elif os.path.isdir(full_path):
-            if not os.path.isfile(os.path.join(full_path, '__init__.py')):
+            if (not namespace and
+                not os.path.isfile(os.path.join(full_path, '__init__.py'))):
                 return None, False
 
             load_tests = None

Misc/NEWS.d/next/Library/2024-09-07-13-57-49.gh-issue-80958.fVYnqV.rst

@@ -0,0 +1 @@
+Restore support for unittest discovery of PEP 420 namespace packages.