diff -r dc65187be892 Lib/unittest/case.py
--- a/Lib/unittest/case.py	Mon Apr 13 11:07:35 2015 -0500
+++ b/Lib/unittest/case.py	Mon Apr 13 11:13:00 2015 -0400
@@ -997,8 +997,10 @@
         if isinstance(expected_regexp, basestring):
             expected_regexp = re.compile(expected_regexp)
         if not expected_regexp.search(text):
-            msg = msg or "Regexp didn't match"
-            msg = '%s: %r not found in %r' % (msg, expected_regexp.pattern, text)
+            standardMsg = "Regex didn't match: %r not found in %r" % (
+                expected_regexp.pattern, text)
+            # _formatMessage ensures the longMessage option is respected
+            msg = self._formatMessage(msg, standardMsg)
             raise self.failureException(msg)
 
     def assertNotRegexpMatches(self, text, unexpected_regexp, msg=None):
@@ -1007,11 +1009,12 @@
             unexpected_regexp = re.compile(unexpected_regexp)
         match = unexpected_regexp.search(text)
         if match:
-            msg = msg or "Regexp matched"
-            msg = '%s: %r matches %r in %r' % (msg,
-                                               text[match.start():match.end()],
-                                               unexpected_regexp.pattern,
-                                               text)
+            standardMsg = 'Regex matched: %r matches %r in %r' % (
+                text[match.start() : match.end()],
+                unexpected_regexp.pattern,
+                text)
+            # _formatMessage ensures the longMessage option is respected
+            msg = self._formatMessage(msg, standardMsg)
             raise self.failureException(msg)
 
 
diff -r dc65187be892 Lib/unittest/test/test_assertions.py
--- a/Lib/unittest/test/test_assertions.py	Mon Apr 13 11:07:35 2015 -0500
+++ b/Lib/unittest/test/test_assertions.py	Mon Apr 13 11:13:00 2015 -0400
@@ -100,7 +100,6 @@
         try:
             self.assertNotRegexpMatches('Ala ma kota', r'k.t', 'Message')
         except self.failureException, e:
-            self.assertIn("'kot'", e.args[0])
             self.assertIn('Message', e.args[0])
         else:
             self.fail('assertNotRegexpMatches should have failed.')
@@ -285,6 +284,20 @@
                              "^unexpectedly identical: None$",
                              "^unexpectedly identical: None : oops$"])
 
+    def testAssertRegex(self):
+        self.assertMessages('assertRegexpMatches', ('foo', 'bar'),
+                            ["^Regex didn't match:",
+                             "^oops$",
+                             "^Regex didn't match:",
+                             "^Regex didn't match: (.*) : oops$"])
+
+    def testAssertNotRegex(self):
+        self.assertMessages('assertNotRegexpMatches', ('foo', 'foo'),
+                            ["^Regex matched:",
+                             "^oops$",
+                             "^Regex matched:",
+                             "^Regex matched: (.*) : oops$"])
+
 
 if __name__ == '__main__':
     unittest.main()