Use MatchesRegex internally in MatchesException.

Change MatchesRegex to have a nicer error message.

NEWS

@@ -4,6 +4,12 @@ testtools NEWS
 NEXT
 ~~~~
 
+Changes
+-------
+
+* ``MatchesRegex`` mismatch now says "<value> does not match <regex>" rather
+  than "<regex> did not match <value>"
+
 Improvements
 ------------
 

testtools/matchers.py

@@ -417,6 +417,8 @@ class MatchesException(Matcher):
         """
         Matcher.__init__(self)
         self.expected = exception
+        if value_re:
+            value_re = MatchesRegex(value_re)
         self.value_re = value_re
         self._is_instance = type(self.expected) not in classtypes()
 
@@ -434,10 +436,7 @@ class MatchesException(Matcher):
                         _error_repr(other[1]), _error_repr(self.expected)))
         elif self.value_re is not None:
             str_exc_value = str(other[1])
-            if not re.match(self.value_re, str_exc_value):
-                return Mismatch(
-                    '"%s" does not match "%s".'
-                    % (str_exc_value, self.value_re))
+            return self.value_re.match(str_exc_value)
 
     def __str__(self):
         if self._is_instance:
@@ -729,7 +728,7 @@ class MatchesRegex(object):
 
     def match(self, value):
         if not re.match(self.pattern, value, self.flags):
-            return Mismatch("%r did not match %r" % (self.pattern, value))
+            return Mismatch("%r does not match %r" % (value, self.pattern))
 
 
 class MatchesSetwise(object):

testtools/tests/test_matchers.py

@@ -257,7 +257,7 @@ class TestMatchesExceptionTypeReInterface(TestCase, TestMatchersInterface):
          MatchesException(Exception))
         ]
     describe_examples = [
-        ('"bar" does not match "fo.".',
+        ("'bar' does not match 'fo.'",
          error_bar, MatchesException(ValueError, "fo.")),
         ]
 
@@ -618,7 +618,7 @@ class TestMatchesRegex(TestCase, TestMatchersInterface):
         ]
 
     describe_examples = [
-        ("'a|b' did not match 'c'", 'c', MatchesRegex('a|b')),
+        ("'c' does not match 'a|b'", 'c', MatchesRegex('a|b')),
         ]