public void SetUp()
        {
            callback = MockRepository.GenerateMock<IDictionaryCallback>();

            dict1 = new Dictionary<string, object>
            {
                {"a", 1},
                {"b", 2},
                {"c", 3}
            };

            dict2 = new Dictionary<string, object>
            {
                {"d", 4},
                {"e", 5},
                {"f", 6}
            };

            dict3 = new Dictionary<string, object>
            {
                {"g", 7},
                {"h", 8},
                {"i", 9}
            };

            aggregate = new AggregateDictionary();
            aggregate.AddLocator(RequestDataSource.Route, key => dict1.ContainsKey(key) ? dict1[key] : null);
            aggregate.AddLocator(RequestDataSource.Request, key => dict2.ContainsKey(key) ? dict2[key] : null);
            aggregate.AddLocator(RequestDataSource.Header, key => dict3.ContainsKey(key) ? dict3[key] : null);
        }