Webster's Dictionary defines testimony as evidence, declaration to prove some fact, a public profession of religious experience.
We need to realize that our mouth testifies about us in how we talk to others (words we use and tone in which we use them). Psalm 119:88 "Quicken me after thy lovingkindness; so shall I keep the testimony of thy mouth." There are those that say they are Christians yet they say filthy things. This may include curse words or dirty of off-color jokes.
Psalm 132:12 "If thy children will keep my covenant and my testimony that I shall teach them their children shall also sit upon thy throne evermore."
Our children and grandchildren (if you have any) are watching us and listening to us when we speak. They will do what we do and say what we say. You will see your testimony played out in them. They figure if it is okay for you to say then it must be okay for them to say it too. That includes those words considered to be light cursing. What we are teaching our children when the Man of God from the Word of God tells us we shouldn't say then we say them...then we are teaching them it isn't important to obey God. And if its okay to disobey God in that area of our lives then it must be okay if we disobey Him in other areas of our lives. What we say and how we say it is very important. It verifies to others what you say you are.
James 1:26 "If any man among you seem to be religious, and bridleth not his tongue, but deceiveth his own heart, this man's religion is in vain."
Whether you are saved and just struggling with your language or you're not saved...think what your testimony is to others if you profess Christ and use the wrong type of language. Also even if no one else is around and we use the wrong type of language remember "The eyes of the LORD are in every place beholding the evil and the good." Proverbs 15:3
We also need to realize our behavior testifies of us. I Peter 1:15-16 "But as he which hath called you is holy, so be ye holy in all manner of conversation: Because it is written, be ye holy; for I am holy." Conversation here in this verse in the Greek is anastrofay which means behavior. God commands us in His Word to be holy and to live holy. Testimony is important to the Lord and it ought to be important to us too. If Jesus lives in our hearts then we take Him everywhere we go. In subjecting ourselves to things we are also subjecting Him to the same things. It grieves the Lord to go some of the places Christians go, to watch some of the things they watch and so on.
We need to remember the only Bible some of those around us are going to see is the Bible we show them in our lives. It is also important to take notice of the way we dress and present ourselves to the world.
Our lives are not ours....it belongs to God and we are to let Him live through us. Be careful of what your testimony is and let it be a walking Bible to those around us that we may show them we are different and give others a testimony that they would desire to have for their own that we might win them to the Lord Jesus Christ.
If your testimony is not what you think Christ would be pleased with then submit yourself to God afresh and anew and get in the Word to find out how He'd have you to live. Its so important to be in Sunday School, church for the preaching of the Word and to study and read and meditate on the Word in order to know how to live a pure and godly life.
The most important thing to remember is that we cannot live a godly Christian life in our own strength....we must let Him live it through us. To do so in our own strength will cause us to fail. When we let Him live His life through us then we will be pleasing Him and our testimony will please Him too.