Testimony must be given for the sake of God even though it is against ourselves, our parents or relatives!

Verse 135 of Chapter 4:

O Believers, be you the standard-bearers of justice and witnesses for the sake of Allah, even though your justice and your evidence might be harmful to yourselves, or to your parents, or to your relatives. It does not matter whether the party concerned is rich or poor: Allah is their greater well-wisher than you; therefore, do not follow your own desire lest you should deviate from doing justice. If you distort your evidence or refrain from the truth, know it well that Allah is fully aware of what you do.