bpo-41403: Improve error message for invalid mock target (GH-30833) (GH-30835)

(cherry picked from commit f7955a8)

Author: iritkatriel

Lib/unittest/mock.py

@@ -1557,9 +1557,9 @@ def stop(self):
 def _get_target(target):
     try:
         target, attribute = target.rsplit('.', 1)
-    except (TypeError, ValueError):
-        raise TypeError("Need a valid target to patch. You supplied: %r" %
-                        (target,))
+    except (TypeError, ValueError, AttributeError):
+        raise TypeError(
+            f"Need a valid target to patch. You supplied: {target!r}")
     getter = lambda: _importer(target)
     return getter, attribute
 

Lib/unittest/test/testmock/testpatch.py

@@ -1933,8 +1933,13 @@ def test(mock):
 
 
     def test_invalid_target(self):
-        with self.assertRaises(TypeError):
-            patch('')
+        class Foo:
+            pass
+
+        for target in ['', 12, Foo()]:
+            with self.subTest(target=target):
+                with self.assertRaises(TypeError):
+                    patch(target)
 
 
     def test_cant_set_kwargs_when_passing_a_mock(self):

Misc/NEWS.d/next/Library/2022-01-23-18-04-45.bpo-41403.SgoHqV.rst

@@ -0,0 +1,3 @@
+Make :meth:`mock.patch` raise a :exc:`TypeError` with a relevant error
+message on invalid arg. Previously it allowed a cryptic
+:exc:`AttributeError` to escape.