Use proper exception type and update changelog

AUTHORS

@@ -9,6 +9,7 @@ Development Lead
 Patches and Suggestions
 ```````````````````````
 
+- Adam Byrtek
 - Adam Zapletal
 - Ali Afshar
 - Chris Edgemon

CHANGES

@@ -11,6 +11,9 @@ Version 0.12
   See pull request ``#1849``.
 - Make ``flask.safe_join`` able to join multiple paths like ``os.path.join``
   (pull request ``#1730``).
+- Added `json` keyword argument to :meth:`flask.testing.FlaskClient.open`
+  (and related ``get``, ``post``, etc.), which makes it more convenient to
+  send JSON requests from the test client.
 
 Version 0.11.2
 --------------

flask/testing.py

@@ -37,7 +37,7 @@ def make_test_environ_builder(app, path='/', base_url=None, json=None, *args, **
 
     if json is not None:
         if 'data' in kwargs:
-            raise RuntimeError('Client cannot provide both `json` and `data`')
+            raise ValueError('Client cannot provide both `json` and `data`')
         kwargs['data'] = json_dumps(json)
 
         # Only set Content-Type when not explicitly provided