True Christian? If there's a true Christian, there must be a false one as well.
But really, either you are or you aren't. What it brings to mind though is that in today's world, there are those who parade around as Christians, but are not.
Paul, Peter, Jesus warned us that this would happen. We will have false teachers, we will have false prophets, we will have false brothers among us; wolves dressed as sheep that desire to devour the flock of God.
The tares are among us and will be separated at the end, the sheep from the goats.
The OP makes me think of this scripture; comforting words from our Lord and Savior.
John 8
31 So Jesus was saying to those Jews who had believed Him, “If you continue in My word, then you are truly disciples of Mine; 32 and you will know the truth, and the truth will make you free.”
John 15:8 My Father is glorified by this, that you bear much fruit, and so prove to be My disciples.