#7031: Add TestCase.assertIsInstance and negated method.

Doc/library/unittest.rst

@@ -955,6 +955,22 @@ Test cases
       .. versionadded:: 2.7
 
 
+   .. method:: assertIsInstance(obj, cls[, msg])
+
+      This signals a test failure if *obj* is not an instance of *cls* (which
+      can be a class or a tuple of classes, as supported by :func:`isinstance`).
+
+      .. versionadded:: 2.7
+
+
+   .. method:: assertNotIsInstance(obj, cls[, msg])
+
+      The inverse of the :meth:`assertIsInstance` method.  This signals a test
+      failure if *obj* is an instance of *cls*.
+
+      .. versionadded:: 2.7
+
+
    .. method:: assertFalse(expr[, msg])
                failIf(expr[, msg])
 

Lib/test/test_unittest.py

@@ -2500,6 +2500,18 @@ class Test_TestCase(TestCase, TestEquality, TestHashing):
         self.assertIsNot(thing, object())
         self.assertRaises(self.failureException, self.assertIsNot, thing, thing)
 
+    def testAssertIsInstance(self):
+        thing = []
+        self.assertIsInstance(thing, list)
+        self.assertRaises(self.failureException, self.assertIsInstance,
+                          thing, dict)
+
+    def testAssertNotIsInstance(self):
+        thing = []
+        self.assertNotIsInstance(thing, dict)
+        self.assertRaises(self.failureException, self.assertNotIsInstance,
+                          thing, list)
+
     def testAssertIn(self):
         animals = {'monkey': 'banana', 'cow': 'grass', 'seal': 'fish'}
 

Lib/unittest/case.py

@@ -817,6 +817,19 @@ class TestCase(object):
             standardMsg = 'unexpectedly None'
             self.fail(self._formatMessage(msg, standardMsg))
 
+    def assertIsInstance(self, obj, cls, msg=None):
+        """Same as self.assertTrue(isinstance(obj, cls)), with a nicer
+        default message."""
+        if not isinstance(obj, cls):
+            standardMsg = '%r is not an instance of %r' % (obj, cls)
+            self.fail(self._formatMessage(msg, standardMsg))
+
+    def assertNotIsInstance(self, obj, cls, msg=None):
+        """Included for symmetry with assertIsInstance."""
+        if isinstance(obj, cls):
+            standardMsg = '%r is an instance of %r' % (obj, cls)
+            self.fail(self._formatMessage(msg, standardMsg))
+
     def assertRaisesRegexp(self, expected_exception, expected_regexp,
                            callable_obj=None, *args, **kwargs):
         """Asserts that the message in a raised exception matches a regexp.