function (res, err) {
     var img;
     if (!err && res.headers['content-type'] === 'image/png') {
         img = mapnik.Image.fromBytes(new Buffer(res.body, 'binary'));
     }
     return callback(err, res, img);
 }
 assert.response(server, requestOptions, expectedResponse, function (res, err) {
     var img;
     if (statusCode === 200) {
         img = mapnik.Image.fromBytes(new Buffer(res.body, 'binary'));
     }
     return callback(err, res, img);
 });
                function checkPreview (err, res) {
                    assert.ifError(err);

                    var next = this;
                    var img = mapnik.Image.fromBytes(new Buffer(res.body, 'binary'));
                    var previewFixturePath = previewFixture(scenario.name);

                    assert.imageIsSimilarToFile(img, previewFixturePath, IMAGE_TOLERANCE, next);
                },
            assert.response(server, request, expectedResponse, function(res, err) {
                assert.ifError(err);

                var image;

                if (isPng) {
                    image = mapnik.Image.fromBytes(new Buffer(res.body, 'binary'));
                }

                next(null, res, image);
            });
 testHelper.deleteRedisKeys({'user:localhost:mapviews:global': 5}, function() {
     return callback(err, mapnik.Image.fromBytes(new Buffer(res.body, 'binary')));
 });