Treat frozenset as a set

Thanks to Brianna Laugher.

_pytest/assertion/util.py

@@ -94,7 +94,7 @@ def assertrepr_compare(config, op, left, right):
     issequence = lambda x: isinstance(x, (list, tuple))
     istext = lambda x: isinstance(x, basestring)
     isdict = lambda x: isinstance(x, dict)
-    isset = lambda x: isinstance(x, set)
+    isset = lambda x: isinstance(x, (set, frozenset))
 
     verbose = config.getoption('verbose')
     explanation = None

testing/test_assertion.py

@@ -99,6 +99,11 @@ class TestAssert_reprcompare:
         expl = callequal(set([0, 1]), set([0, 2]))
         assert len(expl) > 1
 
+    def test_frozenzet(self):
+        expl = callequal(frozenset([0, 1]), set([0, 2]))
+        print expl
+        assert len(expl) > 1
+
     def test_list_tuples(self):
         expl = callequal([], [(1,2)])
         assert len(expl) > 1