Check for a request ctx before using the request.

Use the app json coder when blueprint json coder is set to none.
Revert the failling test to using an app_context
re #1710

flask/json.py

@@ -13,6 +13,7 @@ import uuid
 from datetime import date
 from .globals import current_app, request
 from ._compat import text_type, PY2
+from .ctx import has_request_context
 
 from werkzeug.http import http_date
 from jinja2 import Markup
@@ -94,8 +95,11 @@ class JSONDecoder(_json.JSONDecoder):
 def _dump_arg_defaults(kwargs):
     """Inject default arguments for dump functions."""
     if current_app:
-        bp = current_app.blueprints.get(request.blueprint, None)
+        bp = current_app.blueprints.get(request.blueprint,
-        kwargs.setdefault('cls', bp.json_encoder if bp else current_app.json_encoder)
+                                        None) if has_request_context() else None
+        kwargs.setdefault('cls',
+                          bp.json_encoder if bp and bp.json_encoder
+                          else current_app.json_encoder)
         if not current_app.config['JSON_AS_ASCII']:
             kwargs.setdefault('ensure_ascii', False)
         kwargs.setdefault('sort_keys', current_app.config['JSON_SORT_KEYS'])
@@ -107,8 +111,11 @@ def _dump_arg_defaults(kwargs):
 def _load_arg_defaults(kwargs):
     """Inject default arguments for load functions."""
     if current_app:
-        bp = current_app.blueprints.get(request.blueprint, None)
+        bp = current_app.blueprints.get(request.blueprint,
-        kwargs.setdefault('cls', bp.json_decoder if bp else current_app.json_decoder)
+                                        None) if has_request_context() else None
+        kwargs.setdefault('cls',
+                          bp.json_decoder if bp and bp.json_decoder
+                          else current_app.json_decoder)
     else:
         kwargs.setdefault('cls', JSONDecoder)
 

tests/test_helpers.py

@@ -90,12 +90,12 @@ class TestJSON(object):
         app = flask.Flask(__name__)
 
         app.config['JSON_AS_ASCII'] = True
-        with app.test_request_context():
+        with app.app_context():
             rv = flask.json.dumps(u'\N{SNOWMAN}')
             assert rv == '"\\u2603"'
 
         app.config['JSON_AS_ASCII'] = False
-        with app.test_request_context():
+        with app.app_context():
             rv = flask.json.dumps(u'\N{SNOWMAN}')
             assert rv == u'"\u2603"'