testimony or testimonial

Under normal circumstances, the word you would want would be testimonial. For the native English speaker, this is not confusing. If i find something i like, and speak well of it, i am giving a testimonial. If i am asked to tell the truth about an event which i have seen--the i am being asked to testify, to give testimony.

However, when it come to the religious folks, the language gets somewhat twisted. A Christian speaking of God's love, or mercy, or grace, is said by other Christians to be "testifying." So they would call that testimony. They also abuse the word witness. Speaking to others of God's love or mercy is called "witnessing."

In cases other than that of Christians speaking of their religion, testimony is reporting the truth as you know it about an event, and testimonial is the act of praising a person or a product.

EDIT: At the very beginning of the 17th century, a new translation of the Christian bible was completed at the behest of the king, King James VI and I (meaning he was King James VI of Scotland, but the first King James of England). This translation has come to be known as the King James Bible, or the King James Version. The language of it is actually quite elegant. The use of testimony and witness by Christians is a product of the effect of the KJV on English--in the 17th century, that is how those words were used

This evening, i was reading a biography of Oliver Cromwell (1599-1658) and came across another such example. It is the word discover. At that time, the word discover could mean "to reveal," as well as having the meanings with which we are familiar. There was a satire on Cromwell printed by his enemies, which shows him consulting with "The Devel" (i.e., the Devil, or Satan). The title of the satire is "Olever Cromwell's Cabinet Councell Discovered." (Note that spellings were rather loose in those days.) What it means is "Oliver Cromwell's Cabinet Council Revealed." Of course, this would confuse a modern reader, unless he or she knew how discover was used three and four hundred years ago.