fix assertion rewriting on calls with a double-star arg

CHANGELOG

@@ -1,6 +1,7 @@
 Changes between 2.1.0 and 2.1.1.DEV
 ----------------------------------------------
 
+- fix assertion rewriting on calls with a ** arg
 - don't cache rewritten modules if bytecode generation is disabled
 - fix assertion rewriting in read-only directories
 - fix issue59: provide system-out/err tags for junitxml output

_pytest/assertion/rewrite.py

@@ -514,7 +514,7 @@ class AssertionRewriter(ast.NodeVisitor):
             new_star, expl = self.visit(call.starargs)
             arg_expls.append("*" + expl)
         if call.kwargs:
-            new_kwarg, expl = self.visit(call.kwarg)
+            new_kwarg, expl = self.visit(call.kwargs)
             arg_expls.append("**" + expl)
         expl = "%s(%s)" % (func_expl, ', '.join(arg_expls))
         new_call = ast.Call(new_func, new_args, new_kwargs, new_star, new_kwarg)

testing/test_assertrewrite.py

@@ -195,6 +195,10 @@ class TestAssertionRewrite:
         def f():
             assert g(1, 3, g=23)
         assert getmsg(f, ns) == """assert g(1, 3, g=23)"""
+        def f():
+            x = "a"
+            assert g(**{x : 2})
+        assert getmsg(f, ns) == """assert g(**{'a': 2})"""
 
     def test_attribute(self):
         class X(object):