From 5f5f11faf9de0d8dcbe1a8a4eb35d2a4232d6eaa Mon Sep 17 00:00:00 2001
From: Abraham Toriz Cruz <awonderfulcode@gmail.com>
Date: Tue, 17 Sep 2019 06:16:08 -0500
Subject: [PATCH] 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').
---
 Lib/unittest/mock.py                                      | 2 +-
 Lib/unittest/test/testmock/testmock.py                    | 8 ++++++++
 .../next/Library/2019-09-15-21-31-18.bpo-37828.gLLDX7.rst | 2 ++
 3 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2019-09-15-21-31-18.bpo-37828.gLLDX7.rst

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 74d32af9bf9..4cf8e60ccc1 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -868,7 +868,7 @@ class NonCallableMock(Base):
         """
         if self.call_count == 0:
             msg = ("Expected '%s' to have been called." %
-                   self._mock_name or 'mock')
+                   (self._mock_name or 'mock'))
             raise AssertionError(msg)
 
     def assert_called_once(self):
diff --git a/Lib/unittest/test/testmock/testmock.py b/Lib/unittest/test/testmock/testmock.py
index 581afaaeb81..2bafa8266b6 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()
diff --git a/Misc/NEWS.d/next/Library/2019-09-15-21-31-18.bpo-37828.gLLDX7.rst b/Misc/NEWS.d/next/Library/2019-09-15-21-31-18.bpo-37828.gLLDX7.rst
new file mode 100644
index 00000000000..c364009b240
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-09-15-21-31-18.bpo-37828.gLLDX7.rst
@@ -0,0 +1,2 @@
+Fix default mock name in :meth:`unittest.mock.Mock.assert_called` exceptions.
+Patch by Abraham Toriz Cruz.