Add unit test for loading from JSON
Add unit test for loading from JSON

CesiumGS/cesium,likangning93/cesium,CesiumGS/cesium,CesiumGS/cesium,likangning93/cesium,likangning93/cesium,likangning93/cesium,AnalyticalGraphicsInc/cesium,CesiumGS/cesium,CesiumGS/cesium,AnalyticalGraphicsInc/cesium,likangning93/cesium