Closes issue 15323. Improve failure message of Mock.assert_called_once_with

NEWS

+- Issue #15323: improve failure message of Mock.assert_called_once_with
+
 - Issue #14857: fix regression in references to PEP 3135 implicit __class__
   closure variable (Reopens issue #12370)
 

mock.py

@@ -864,8 +864,8 @@ class NonCallableMock(Base):
         arguments."""
         self = _mock_self
         if not self.call_count == 1:
-            msg = ("Expected to be called once. Called %s times." %
-                   self.call_count)
+            msg = ("Expected '%s' to be called once. Called %s times." %
+                   (self._mock_name or 'mock', self.call_count))
             raise AssertionError(msg)
         return self.assert_called_with(*args, **kwargs)
 

tests/testmock.py

@@ -486,6 +486,13 @@ class MockTest(unittest.TestCase):
                                 mock.assert_called_with)
 
 
+    def test_assert_called_once_with_message(self):
+        mock = Mock(name='geoffrey')
+        self.assertRaisesRegex(AssertionError,
+                     r"Expected 'geoffrey' to be called once\.",
+                     mock.assert_called_once_with)
+
+
     def test__name__(self):
         mock = Mock()
         self.assertRaises(AttributeError, lambda: mock.__name__)