add code coverage reporting

circle.yml

@@ -1,3 +1,11 @@
 dependencies:
   pre:
-    - pip install -r requirements.txt
+    - pip install -r requirements.txt
+
+test:
+  override:
+    - coverage run test.py
+  post:
+    - mkdir -p $CIRCLE_ARTIFACTS/coverage-html
+    - coverage html -d $CIRCLE_ARTIFACTS/coverage-html
+    - mv .coverage $CIRCLE_ARTIFACTS

requirements.txt

@@ -1,2 +1,3 @@
 requests
-mock
+mock
+coverage