A Pharisee’s Test for Catholics, Protestants, Mormons & Muslims

In Acts 5, when the Apostles are on trial before the Sanhedrin, a Pharisee named Gamaliel (the same Gamaliel that St. Paul studied under) provided a simple test to determine if a religion really came from God or not. So what was his test, and what does it mean for the credibility and legitimacy of Catholicism, Protestantism, Mormonism, and Islam?