gh-113569: Display calls in Mock.assert_has_calls failure when empty

Lib/test/test_unittest/testmock/testmock.py

@@ -1547,6 +1547,8 @@ def f(x=None): pass
         mock = Mock(spec=f)
         mock(1)
 
+        uncalled_mock = Mock()
+
         with self.assertRaisesRegex(
                 AssertionError,
                 '^{}$'.format(
@@ -1556,6 +1558,14 @@ def f(x=None): pass
             mock.assert_has_calls([call()])
         self.assertIsNone(cm.exception.__cause__)
 
+        with self.assertRaisesRegex(
+                AssertionError,
+                '^{}$'.format(
+                    re.escape('Calls not found.\n'
+                              'Expected: [call()]\n'
+                              '  Actual: []'))) as cm:
+            uncalled_mock.assert_has_calls([call()])
+        self.assertIsNone(cm.exception.__cause__)
 
         with self.assertRaisesRegex(
                 AssertionError,

Lib/unittest/mock.py

@@ -1011,7 +1011,7 @@ def assert_has_calls(self, calls, any_order=False):
                 raise AssertionError(
                     f'{problem}\n'
                     f'Expected: {_CallList(calls)}'
-                    f'{self._calls_repr(prefix="  Actual").rstrip(".")}'
+                    f'{self._calls_repr(prefix="  Actual", display_empty=True).rstrip(".")}'
                 ) from cause
             return
 
@@ -1085,15 +1085,15 @@ def _get_child_mock(self, /, **kw):
         return klass(**kw)
 
 
-    def _calls_repr(self, prefix="Calls"):
+    def _calls_repr(self, prefix="Calls", display_empty=False):
         """Renders self.mock_calls as a string.
 
         Example: "\nCalls: [call(1), call(2)]."
 
         If self.mock_calls is empty, an empty string is returned. The
         output will be truncated if very long.
         """
-        if not self.mock_calls:
+        if not self.mock_calls and not display_empty:
             return ""
         return f"\n{prefix}: {safe_repr(self.mock_calls)}."
 

Misc/NEWS.d/next/Library/2023-12-29-17-57-45.gh-issue-113569.qcRCEI.rst

@@ -0,0 +1,2 @@
+Display list of actual calls in unittest `Mock.assert_has_calls` failure
+message even if empty.