android studio单元测试 无法进入网络请求的回调

//在网络发送请求前添加拦截：
final CountDownLatch signal = new CountDownLatch(1);
NetHelper.getInstance().userLogin("13381033767", MD5.getMD5Str("123456"),
new ResponseCallback() {
@Override
public
void onSuccess(JSONObject
response) throws JSONException
{
Log.i("---test2", response.toString());
Log.i("---test3", "succeed");
signal.countDown();
}

@Override
public
void onFailure(VolleyError
error) {
Log.i("---test2", error.toString());
signal.countDown();
}
});

//等待响应

try {
signal.await();
} catch (InterruptedException
e) {
e.printStackTrace();
}

如果报 junit.framework.AssertionFailedError错误，在build.gradle中添加
defaultConfig { 
// ...... 
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner" 
}
dependencies {
// ...... 
androidTestCompile 'com.android.support.test:runner:0.3'
}