Testimony and Conversion...

Testimony is personal knowledge of spiritual truth obtained by revelation. Conversion is an enlarging, a deepening, and a broadening of the under-girding base of testimony. Conversion is an offering of self, of love, and of loyalty we give to God in gratitude for the gift of testimony. Knowing that the gospel is true is the essence of a testimony. Consistently being true to the gospel is the essence of conversion. 
~ Elder David A. Bednar ("Converted Unto the Lord," Ensign, Nov. 2012) 

To testify is to know and declare. The gospel challenges us to be "converted", which requires us to do and become. 
~ Elder Dallin H.Oaks ('The Challenge to Become" Ensign, Nov. 2000)