bpo-37828: Fix default mock_name in unittest.mock.assert_called error (GH-16166)

In the format string for assert_called the evaluation order is incorrect and hence for mock's without name, 'None' is printed whereas it should be 'mock' like for other messages. The error message is ("Expected '%s' to have been called." % self._mock_name or 'mock').

1 files changed, 8 insertions, 0 deletions

diff --git a/Lib/unittest/test/testmock/testmock.py b/Lib/unittest/test/testmock/testmock.py
index 581afaaeb8..2bafa8266b 100644
--- a/Lib/unittest/test/testmock/testmock.py
+++ b/Lib/unittest/test/testmock/testmock.py
@@ -396,6 +396,14 @@ class MockTest(unittest.TestCase):
         _check(mock)
 
 
+    def test_assert_called_exception_message(self):
+        msg = "Expected '{0}' to have been called"
+        with self.assertRaisesRegex(AssertionError, msg.format('mock')):
+            Mock().assert_called()
+        with self.assertRaisesRegex(AssertionError, msg.format('test_name')):
+            Mock(name="test_name").assert_called()
+
+
     def test_assert_called_once_with(self):
         mock = Mock()
         mock()