Is voluntarily refraining from testifying for a colleague and concealing it from the court, unless compelled, considered concealing testimony and a sin? And is the "caller" intended in the verse, "And let witnesses not refuse when they are called upon," the rights holder or the judge?

If it is permissible for the female employee to sue her employer in a case of dismissal, then her colleague must testify for her if required, provided her testimony is beneficial and she would not incur harm, and she was asked to testify. However, if it is not legally permissible for the employee to sue her employer, then her colleague is not allowed to assist her.