Actually hand-spin and use a tzinfo subclass

This is for Python 2.x compatibility.

Suggested-by: David Lord <davidism@gmail.com>

tests/test_helpers.py

@@ -34,6 +34,27 @@ def has_encoding(name):
         return False
 
 
+class FixedOffset(datetime.tzinfo):
+    """Fixed offset in hours east from UTC.
+
+    This is a slight adaptation of the ``FixedOffset`` example found in
+    https://docs.python.org/2.7/library/datetime.html.
+    """
+
+    def __init__(self, hours, name):
+        self.__offset = datetime.timedelta(hours=hours)
+        self.__name = name
+
+    def utcoffset(self, dt):
+        return self.__offset
+
+    def tzname(self, dt):
+        return self.__name
+
+    def dst(self, dt):
+        return datetime.timedelta()
+
+
 class TestJSON(object):
     def test_ignore_cached_json(self, app):
         with app.test_request_context('/', method='POST', data='malformed',
@@ -180,9 +201,9 @@ class TestJSON(object):
     @pytest.mark.parametrize('tz', (('UTC', 0), ('PST', -8), ('KST', 9)))
     def test_jsonify_aware_datetimes(self, tz):
         """Test if aware datetime.datetime objects are converted into GMT."""
-        tzinfo = datetime.timezone(datetime.timedelta(hours=tz[1]), name=tz[0])
+        tzinfo = FixedOffset(hours=tz[1], name=tz[0])
         dt = datetime.datetime(2017, 1, 1, 12, 34, 56, tzinfo=tzinfo)
-        gmt = datetime.timezone(datetime.timedelta(), name='GMT')
+        gmt = FixedOffset(hours=0, name='GMT')
         expected = dt.astimezone(gmt).strftime('"%a, %d %b %Y %H:%M:%S %Z"')
         assert flask.json.JSONEncoder().encode(dt) == expected