reorganize tests, start using pytest

tests/utils.py

@@ -0,0 +1,13 @@
+import json
+
+def assert_httpbin_responses_equal(body1, body2):
+    """
+    httpbin.org returns a different `origin` header 
+    each time, so strip this out since it makes testing
+    difficult.
+    """
+    body1, body2 = json.loads(body1), json.loads(body2)
+    del body1['origin']
+    del body2['origin']
+    assert body1 == body2
+