Implement KeysEqual matcher.

testtools/matchers.py

@@ -342,6 +342,34 @@ class StartsWith(Matcher):
         return None
 
 
+class KeysEqual(Matcher):
+    """Checks whether a dict has particular keys."""
+
+    def __init__(self, *expected):
+        """Create a `KeysEqual` Matcher.
+
+        :param *expected: The keys the dict is expected to have.  If a dict,
+            then we use the keys of that dict, if a collection, we assume it
+            is a collection of expected keys.
+        """
+        try:
+            self.expected = expected.keys()
+        except AttributeError:
+            self.expected = list(expected)
+
+    def __str__(self):
+        return "KeysEqual(%s)" % ', '.join(map(repr, self.expected))
+
+    def match(self, matchee):
+        expected = sorted(self.expected)
+        matched = Equals(expected).match(sorted(matchee.keys()))
+        if matched:
+            return AnnotatedMismatch(
+                'Keys not equal',
+                _BinaryMismatch(expected, 'does not match', matchee))
+        return None
+
+
 class Annotate(object):
     """Annotates a matcher with a descriptive string.
 

testtools/tests/test_matchers.py

@@ -13,6 +13,7 @@ from testtools.matchers import (
     Equals,
     DocTestMatches,
     DoesNotStartWith,
+    KeysEqual,
     Is,
     LessThan,
     MatchesAny,
@@ -211,6 +212,31 @@ class TestMatchesAllInterface(TestCase, TestMatchersInterface):
                           1, MatchesAll(NotEquals(1), NotEquals(2)))]
 
 
+class TestKeysEqual(TestCase, TestMatchersInterface):
+
+    matches_matcher = KeysEqual('foo', 'bar')
+    matches_matches = [
+        {'foo': 0, 'bar': 1},
+        ]
+    matches_mismatches = [
+        {},
+        {'foo': 0},
+        {'bar': 1},
+        {'foo': 0, 'bar': 1, 'baz': 2},
+        {'a': None, 'b': None, 'c': None},
+        ]
+
+    str_examples = [
+        ("KeysEqual('foo', 'bar')", KeysEqual('foo', 'bar')),
+        ]
+
+    describe_examples = [
+        ("['bar', 'foo'] does not match {'baz': 2, 'foo': 0, 'bar': 1}: "
+         "Keys not equal",
+         {'foo': 0, 'bar': 1, 'baz': 2}, KeysEqual('foo', 'bar')),
+        ]
+
+
 class TestAnnotate(TestCase, TestMatchersInterface):
 
     matches_matcher = Annotate("foo", Equals(1))