The Bible says we should have inner assurance from the Holy Spirit:

"Hereby know we that we dwell in him, and he in us, because he hath given us of his Spirit"  "The Spirit itself beareth witness with our spirit, that we are the children of God"  “My sheep hear my voice, and I know them, and they follow me:”  "And he that keepeth his commandments dwelleth in him, and he in him. And hereby we know that he abideth in us, by the Spirit which he hath given us." “He that believeth on the Son of God hath the witness in himself:” “And the work of righteousness shall be peace; and the effect of righteousness quietness and assurance for ever.”  “Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?”

Have I experienced the Holy Spirit? (NOT in the charismatic sense)  Or do I just know ABOUT Him and believe that I have Him inside of me because I can point to a scripture verse that says that He should be there?  Intellectual (pretend) 'salvation'; versus Spirit wrought illumination.  Mental assent to facts; versus Spirit wrought illumination.  The difference is Life and death.

The only thing that ultimately matters that we each must ask ourselves is: Am I a reprobate?
Do I "know" (the word “know” means an intimate personal knowledge, the same "know" as used for marriage)?  Assurance comes from inside - from the Holy Spirit.  I know that He is there because He talks with me and teaches me, and manifests Himself to me, and helps me to yield the fruits of the Spirit as I walk the "narrow way" in strict obedience; not because I can point to a Bible verse that says that He should be there.

The hymn says: "And He walks with me and He talks with me and He tells me I am His own".  This is not pretend.  Or beautiful symbolism or poetry:  "My sheep hear my voice".

“Now if any man have not the Spirit of Christ, he is none of his.”

If someone doesn't know that they have the Holy Spirit on a level that "passeth knowledge" (not simply from a mental/intellectual pointing to a Bible verse) than He is not born again, not a believer, and is not abiding in eternal life.
 
Don't delude yourself. 
 

The gate is "strait" and "few there be who find it".

"Strive to enter in at the strait gate".