Better content header error and slight refactor of test helper

backdrop/write/api.py

@@ -253,7 +253,8 @@ def _empty_data_set(data_set_config):
 
 def listify_json(data):
     if data is None:
-        raise ValidationError("Request must be JSON")
+        raise ValidationError(
+            "Expected header: Content-type: application/json")
 
     if isinstance(data, list):
         return data

tests/support/test_helpers.py

@@ -58,6 +58,9 @@ def has_header(name, value):
 
 
 class IsErrorResponse(BaseMatcher):
+    def __init__(self, message):
+        self.message = message
+
     def _matches(self, response):
         try:
             data = json.loads(response.data)
@@ -66,18 +69,25 @@ def _matches(self, response):
             # it should not fail with out a message
             if not data.get('message'):
                 return False
+            if self.message and not data.get('message') == self.message:
+                return False
             return True
         except ValueError:
             return False
 
     def describe_to(self, description):
+        if not self.message:
+            description_message = 'error response with any error message'
+        else:
+            description_message = 'error response with message: "{}"'.format(
+                self.message)
         description.append_text(
-            'error response'
+            description_message
         )
 
 
-def is_error_response():
-    return IsErrorResponse()
+def is_error_response(message=None):
+    return IsErrorResponse(message)
 
 
 def d_tz(year, month, day, hour=0, minute=0, seconds=0, tzinfo=None):

tests/write/test_flask_integration.py

@@ -69,7 +69,7 @@ def test_request_must_be_json(self):
         )
 
         assert_that( response, is_bad_request())
-        assert_that( response, is_error_response())
+        assert_that( response, is_error_response("ValidationError('Expected header: Content-type: application/json',)"))
 
     @fake_data_set_exists("foo_data_set", bearer_token="foo_data_set-bearer-token")
     @patch("backdrop.core.data_set.DataSet.store")