Nicer error message for regex fail.

testtools/matchers.py

@@ -730,7 +730,8 @@ class MatchesRegex(object):
 
     def match(self, value):
         if not re.match(self.pattern, value, self.flags):
-            return Mismatch("%r does not match %r" % (value, self.pattern))
+            return Mismatch("%r does not match /%s/" % (
+                    value, self.pattern))
 
 
 class MatchesSetwise(object):

testtools/tests/test_matchers.py

@@ -258,7 +258,7 @@ class TestMatchesExceptionTypeReInterface(TestCase, TestMatchersInterface):
          MatchesException(Exception, 'fo.'))
         ]
     describe_examples = [
-        ("'bar' does not match 'fo.'",
+        ("'bar' does not match /fo./",
          error_bar, MatchesException(ValueError, "fo.")),
         ]
 
@@ -639,7 +639,8 @@ class TestMatchesRegex(TestCase, TestMatchersInterface):
         ]
 
     describe_examples = [
-        ("'c' does not match 'a|b'", 'c', MatchesRegex('a|b')),
+        ("'c' does not match /a|b/", 'c', MatchesRegex('a|b')),
+        ("'c' does not match /a\d/", 'c', MatchesRegex(r'a\d')),
         ]
 
 

testtools/tests/test_with_with.py

@@ -32,7 +32,7 @@ class TestExpectedException(TestCase):
                 raise ValueError('mismatch')
         except AssertionError:
             e = sys.exc_info()[1]
-            self.assertEqual("'mismatch' does not match 'tes.'", str(e))
+            self.assertEqual("'mismatch' does not match /tes./", str(e))
         else:
             self.fail('AssertionError not raised.')