Android已连接AndroidTest：未找到测试

Question

Android已连接AndroidTest：未找到测试

gradle :aar-lib:connectedAndroidTest

com.android.builder.testing.ConnectedDevice > No tests found.
FAILED  No tests found. This usually means that your test classes 
are not in the form that your test runner expects (e.g. don't 
inherit from TestCase or lack @Test annotations).

测试类别：

@RunWith(AndroidJUnit4.class)
public class FooTest {

    @Test
    public void testFoo() {
    ....
    }
}

看着测试APK，它包含测试类。