Do Not Test Behavior as a Show of Salvific Belief but Test the Behavior of Your Christian Sibling
Pressing a Christian sibling to show that they believe is against the Bible's teaching of accepting the mere word of the sibling that they repent seven times in a day. Believing is all that's necessary to believe, and you cannot monitor another's heart - they must tell you whether or not they believe. There is a thing that is a response to belief that can be heard by others - verbally confessing Master Jesus. That's the action that goes with belief of the tenets of salvation doctrine that Paul learned and taught, and it has nothing at all to do with sin, so that the old standard some congregations have had to force certain behaviors from Christians in order to ascertain whether or not they are siblings in Christ is wrong. However, monitoring behavior to know whether to rebuke a sibling in Christ and to shun them - but as a sibling and not as an enemy - is biblical and it is right to do that, according to the Scriptures.