[3.14] gh-138729: Cover inspect.formatannotationrelativeto with tests (GH-138730) (GH-138747)

(cherry picked from commit f5fa336)

Co-authored-by: sobolevn <mail@sobolevn.me>

Author: miss-islington

Lib/test/test_inspect/test_inspect.py

@@ -1755,14 +1755,55 @@ class C(metaclass=M):
 
 class TestFormatAnnotation(unittest.TestCase):
     def test_typing_replacement(self):
-        from test.typinganndata.ann_module9 import ann, ann1
+        from test.typinganndata.ann_module9 import A, ann, ann1
         self.assertEqual(inspect.formatannotation(ann), 'List[str] | int')
         self.assertEqual(inspect.formatannotation(ann1), 'List[testModule.typing.A] | int')
 
+        self.assertEqual(inspect.formatannotation(A, 'testModule.typing'), 'A')
+        self.assertEqual(inspect.formatannotation(A, 'other'), 'testModule.typing.A')
+        self.assertEqual(
+            inspect.formatannotation(ann1, 'testModule.typing'),
+            'List[testModule.typing.A] | int',
+        )
+
     def test_forwardref(self):
         fwdref = ForwardRef('fwdref')
         self.assertEqual(inspect.formatannotation(fwdref), 'fwdref')
 
+    def test_formatannotationrelativeto(self):
+        from test.typinganndata.ann_module9 import A, ann1
+
+        # Builtin types:
+        self.assertEqual(
+            inspect.formatannotationrelativeto(object)(type),
+            'type',
+        )
+
+        # Custom types:
+        self.assertEqual(
+            inspect.formatannotationrelativeto(None)(A),
+            'testModule.typing.A',
+        )
+
+        class B: ...
+        B.__module__ = 'testModule.typing'
+
+        self.assertEqual(
+            inspect.formatannotationrelativeto(B)(A),
+            'A',
+        )
+
+        self.assertEqual(
+            inspect.formatannotationrelativeto(object)(A),
+            'testModule.typing.A',
+        )
+
+        # Not an instance of "type":
+        self.assertEqual(
+            inspect.formatannotationrelativeto(A)(ann1),
+            'List[testModule.typing.A] | int',
+        )
+
 
 class TestIsMethodDescriptor(unittest.TestCase):