### Question:
AuthenticationResultHandler { public static AuthenticationResultHandler handler() { return sHandler; } private  AuthenticationResultHandler(); static AuthenticationResultHandler handler(); void setAuthenticationListener(AuthResultListener listener); void onActivityResult(int requestCode, int resultCode, Intent data); @VisibleForTesting
    public AuthResultListener mResultListener; @VisibleForTesting
    public StateResult mCachedResult; @VisibleForTesting
    public ResultType mCachedResultType; }### Answer:
@Test public void handler() { AuthenticationResultHandler handler1 = AuthenticationResultHandler.handler(); assertNotNull(handler1); AuthenticationResultHandler handler2 = AuthenticationResultHandler.handler(); assertNotNull(handler2); assertEquals(handler1, handler2); }