[hypatiadotca]

The standard you walk past is the standard you accept. (a line from https://www.youtube.com/watch?v=QaqpoeVgr8U , if you've not seen it)

Can you live with yourself ethically if you don't testify?

Are there ways that telling the truth about what you witnessed could actually be an advantage to your career?

Say, for example, that you witnessed sexual harassment and were put on the stand to talk about that. Sure, there may be some shitweasel who won't hire you because you "snitched" - but there may be a woman founder of a healthier and more profitable company (http://qz.com/361602/companies-run-by-women-perform-better/ , just sayin') who takes your having testified as a positive, rather than a negative, signal.

Integrity counts for a lot. If someone doesn't want to hire you because you showed integrity under difficult circumstances, did you really want to work for them in the first place?

Now if you're worried about testifying because you yourself behaved unethically, that's a whole other story.