diff -r 1ba0deb52223 -r f5bd331d0156 Lib/unittest/mock.py
--- a/Lib/unittest/mock.py	Wed Feb 10 22:58:18 2016 +0000
+++ b/Lib/unittest/mock.py	Fri Feb 12 10:06:52 2016 +1100
@@ -772,6 +772,24 @@
                    (self._mock_name or 'mock', self.call_count))
             raise AssertionError(msg)
 
+    def assert_called(_mock_self):
+        """assert that the mock was called at least once
+        """
+        self = _mock_self
+        if self.call_count == 0:
+            msg = ("Expected '%s' to have been called." %
+                   self._mock_name or 'mock')
+            raise AssertionError(msg)
+
+    def assert_called_once(_mock_self):
+        """assert that the mock was called only once.
+        """
+        self = _mock_self
+        if not self.call_count == 1:
+            msg = ("Expected '%s' to be called once. Called %s times." %
+                   (self._mock_name or 'mock', self.call_count))
+            raise AssertionError(msg)
+
     def assert_called_with(_mock_self, *args, **kwargs):
         """assert that the mock was called with the specified arguments.
 
diff -r 1ba0deb52223 -r f5bd331d0156 Lib/unittest/test/testmock/testmock.py
--- a/Lib/unittest/test/testmock/testmock.py	Wed Feb 10 22:58:18 2016 +0000
+++ b/Lib/unittest/test/testmock/testmock.py	Fri Feb 12 10:06:52 2016 +1100
@@ -1222,6 +1222,25 @@
         with self.assertRaises(AssertionError):
             m.hello.assert_not_called()
 
+    #Issue26323
+    def test_assert_called(self):
+        m = Mock()
+        with self.assertRaises(AssertionError):
+            m.hello.assert_called()
+        m.hello()
+        m.hello.assert_called()
+
+    #Issue26323
+    def test_assert_called_once(self):
+        m = Mock()
+        m.hello()
+        m.hello()
+        with self.assertRaises(AssertionError):
+            m.hello.assert_called_once()
+        m.reset_mock()
+        m.hello()
+        m.hello.assert_called_once()
+
     #Issue21256 printout of keyword args should be in deterministic order
     def test_sorted_call_signature(self):
         m = Mock()