TEST: Add test for parameter_space ordering.

tests/test_test_utils.py

@@ -14,16 +14,24 @@ class TestParameterSpace(TestCase):
     @classmethod
     def setUpClass(cls):
         cls.xy_invocations = []
+        cls.yx_invocations = []
 
     @classmethod
     def tearDownClass(cls):
         # This is the only actual test here.
         assert cls.xy_invocations == list(product(cls.x_args, cls.y_args))
+        assert cls.yx_invocations == list(product(cls.y_args, cls.x_args))
 
     @parameter_space(x=x_args, y=y_args)
     def test_xy(self, x, y):
         self.xy_invocations.append((x, y))
 
+    @parameter_space(x=x_args, y=y_args)
+    def test_yx(self, y, x):
+        # Ensure that product is called with args in the order that they appear
+        # in the function's parameter list.
+        self.yx_invocations.append((y, x))
+
     def test_nothing(self):
         # Ensure that there's at least one "real" test in the class, or else
         # our {setUp,tearDown}Class won't be called if, for example,