If the confession of the Christian is, "Jesus is Lord," then I offer that there is one litmus test for a person's Christianity. Any guesses?
Church attendance? Bible study? Time in prayer? Serving the poor? Helping the weak?
Well, mostly no. Those could be expressions of a person's Christianity but they're not the litmus test for it. Any more guesses?
How about this: obedience.
Listen to Jesus, the One we follow: "Why do you call me, 'Lord! Lord!' and do not do what I say?" (Luke 6.46).
For those who want to follow Jesus, claim His name, receive His salvation, and live with Him forever, the one thing that we can look to in order to know if we're doing those things or not is the trajectory of our obedience. Are we doing what Jesus said to do? Are we doing what Jesus said is best to do? Are we doing what Jesus said we must do?
Nothing else can test the state of our Christianity like obedience can. And it's self-deceptive to test it by another standard.
But that's just me thinking thoughts.