It’s never been demanded for an professional boxing match before. Mayweather came up with this to duck the fight. He needed something, because he believes he would lose, and I believe he is correct.
Mayweather’s apparent objective is to tarnish Manny Pacquiao without fighting him, and it looks as though he is succeeding due to the legion of suspicious people willing to believe the worst about anyone.
Manny Pacquiao has never been suspected of using illegal substances by anyone, and he is quite right to sue. His reputation has been tarnished by slander, as the posts on this thread testify.