Hi rogersan,
what is the response under your Test Request?
And what is the instruction you post in the test request? 1 and 0 ? or ON and OFF?
In fact , even though there are four pins in the digital 0(3V3, GND,and two IO pins) ,some of them may be NC when it is setted as a general digital output, according to the configuration of grove interface. I have test that the pin 12 is NC.And the pin 14 is HIGH when I post 1, then it turns LOW when I post 0. 
Every thing goes well.