pythongh-122255: Add black box tests in test_warnings (pythonGH-122227)

They are similar to white box tests for pythongh-86298 in test_importlib.
(cherry picked from commit fe13c9b)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Author: serhiy-storchaka

Lib/test/test_warnings/__init__.py

@@ -611,6 +611,97 @@ class NonWarningSubclass:
                 self.module.warn('good warning category', MyWarningClass)
             self.assertIsInstance(cm.warning, Warning)
 
+    def check_module_globals(self, module_globals):
+        with original_warnings.catch_warnings(module=self.module, record=True) as w:
+            self.module.filterwarnings('default')
+            self.module.warn_explicit(
+                'eggs', UserWarning, 'bar', 1,
+                module_globals=module_globals)
+        self.assertEqual(len(w), 1)
+        self.assertEqual(w[0].category, UserWarning)
+        self.assertEqual(str(w[0].message), 'eggs')
+
+    def check_module_globals_error(self, module_globals, errmsg, errtype=ValueError):
+        if self.module is py_warnings:
+            self.check_module_globals(module_globals)
+            return
+        with original_warnings.catch_warnings(module=self.module, record=True) as w:
+            self.module.filterwarnings('always')
+            with self.assertRaisesRegex(errtype, re.escape(errmsg)):
+                self.module.warn_explicit(
+                    'eggs', UserWarning, 'bar', 1,
+                    module_globals=module_globals)
+        self.assertEqual(len(w), 0)
+
+    def check_module_globals_deprecated(self, module_globals, msg):
+        if self.module is py_warnings:
+            self.check_module_globals(module_globals)
+            return
+        with original_warnings.catch_warnings(module=self.module, record=True) as w:
+            self.module.filterwarnings('always')
+            self.module.warn_explicit(
+                'eggs', UserWarning, 'bar', 1,
+                module_globals=module_globals)
+        self.assertEqual(len(w), 2)
+        self.assertEqual(w[0].category, DeprecationWarning)
+        self.assertEqual(str(w[0].message), msg)
+        self.assertEqual(w[1].category, UserWarning)
+        self.assertEqual(str(w[1].message), 'eggs')
+
+    def test_gh86298_no_loader_and_no_spec(self):
+        self.check_module_globals({'__name__': 'bar'})
+
+    def test_gh86298_loader_is_none_and_no_spec(self):
+        self.check_module_globals({'__name__': 'bar', '__loader__': None})
+
+    def test_gh86298_no_loader_and_spec_is_none(self):
+        self.check_module_globals_error(
+            {'__name__': 'bar', '__spec__': None},
+            'Module globals is missing a __spec__.loader')
+
+    def test_gh86298_loader_is_none_and_spec_is_none(self):
+        self.check_module_globals_error(
+            {'__name__': 'bar', '__loader__': None, '__spec__': None},
+            'Module globals is missing a __spec__.loader')
+
+    def test_gh86298_loader_is_none_and_spec_loader_is_none(self):
+        self.check_module_globals_error(
+            {'__name__': 'bar', '__loader__': None,
+             '__spec__': types.SimpleNamespace(loader=None)},
+            'Module globals is missing a __spec__.loader')
+
+    def test_gh86298_no_spec(self):
+        self.check_module_globals_deprecated(
+            {'__name__': 'bar', '__loader__': object()},
+            'Module globals is missing a __spec__.loader')
+
+    def test_gh86298_spec_is_none(self):
+        self.check_module_globals_deprecated(
+            {'__name__': 'bar', '__loader__': object(), '__spec__': None},
+            'Module globals is missing a __spec__.loader')
+
+    def test_gh86298_no_spec_loader(self):
+        self.check_module_globals_deprecated(
+            {'__name__': 'bar', '__loader__': object(),
+             '__spec__': types.SimpleNamespace()},
+            'Module globals is missing a __spec__.loader')
+
+    def test_gh86298_loader_and_spec_loader_disagree(self):
+        self.check_module_globals_deprecated(
+            {'__name__': 'bar', '__loader__': object(),
+             '__spec__': types.SimpleNamespace(loader=object())},
+            'Module globals; __loader__ != __spec__.loader')
+
+    def test_gh86298_no_loader_and_no_spec_loader(self):
+        self.check_module_globals_error(
+            {'__name__': 'bar', '__spec__': types.SimpleNamespace()},
+            'Module globals is missing a __spec__.loader', AttributeError)
+
+    def test_gh86298_no_loader_with_spec_loader_okay(self):
+        self.check_module_globals(
+            {'__name__': 'bar',
+             '__spec__': types.SimpleNamespace(loader=object())})
+
 class CWarnTests(WarnTests, unittest.TestCase):
     module = c_warnings