bpo-29642: Load tests from implicit packages.

Implicit PEP-420-style packages (i.e. missing __init__.py) were omitted,
and this commit enables searching for tests in them.

Author: andreif

Doc/library/unittest.rst

@@ -1674,7 +1674,8 @@ Loading and running tests
       the import failure is due to :exc:`SkipTest` being raised, it will be
       recorded as a skip instead of an error.
 
-      If a package (a directory containing a file named :file:`__init__.py`) is
+      If a package (a directory containing a file named :file:`__init__.py` or
+      a :term:`namespace package <namespace package>`) is
       found, the package will be checked for a ``load_tests`` function. If this
       exists then it will be called
       ``package.load_tests(loader, tests, pattern)``. Test discovery takes care

Lib/unittest/loader.py

@@ -241,7 +241,7 @@ def discover(self, start_dir, pattern='test*.py', top_level_dir=None):
         If the start directory is not the top level directory then the top
         level directory must be specified separately.
 
-        If a test package name (directory with '__init__.py') matches the
+        If a test package name (directory with or w/o '__init__.py') matches the
         pattern then the package will be checked for a 'load_tests' function. If
         this exists then it will be called with (loader, tests, pattern) unless
         the package has already had load_tests called from the same discovery
@@ -282,8 +282,6 @@ def discover(self, start_dir, pattern='test*.py', top_level_dir=None):
         tests = []
         if os.path.isdir(os.path.abspath(start_dir)):
             start_dir = os.path.abspath(start_dir)
-            if start_dir != top_level_dir:
-                is_not_importable = not os.path.isfile(os.path.join(start_dir, '__init__.py'))
         else:
             # support for discovery from dotted module names
             try:
@@ -451,12 +449,6 @@ def _find_test_path(self, full_path, pattern, namespace=False):
                         msg % (mod_name, module_dir, expected_dir))
                 return self.loadTestsFromModule(module, pattern=pattern), False
         elif os.path.isdir(full_path):
-            if (not namespace and
-                not os.path.isfile(os.path.join(full_path, '__init__.py'))):
-                return None, False
-
-            load_tests = None
-            tests = None
             name = self._get_name_from_path(full_path)
             try:
                 package = self._get_module_from_name(name)

Lib/unittest/test/test_discovery.py

@@ -54,7 +54,7 @@ def restore_isdir():
 
         path_lists = [['test2.py', 'test1.py', 'not_a_test.py', 'test_dir',
                        'test.foo', 'test-not-a-module.py', 'another_dir'],
-                      ['test4.py', 'test3.py', ]]
+                      [], ['test4.py', 'test3.py']]
         os.listdir = lambda path: path_lists.pop(0)
         self.addCleanup(restore_listdir)
 
@@ -65,7 +65,7 @@ def isdir(path):
 
         def isfile(path):
             # another_dir is not a package and so shouldn't be recursed into
-            return not path.endswith('dir') and not 'another_dir' in path
+            return not path.endswith('dir') and 'another_dir' not in path
         os.path.isfile = isfile
         self.addCleanup(restore_isfile)
 
@@ -85,7 +85,7 @@ def loadTestsFromModule(module, pattern=None):
         # The test suites found should be sorted alphabetically for reliable
         # execution order.
         expected = [[name + ' module tests'] for name in
-                    ('test1', 'test2', 'test_dir')]
+                    ('another_dir', 'test1', 'test2', 'test_dir')]
         expected.extend([[('test_dir.%s' % name) + ' module tests'] for name in
                     ('test3', 'test4')])
         self.assertEqual(suite, expected)