Is it permissible for a woman to undergo a test to prove her chastity, and is this considered to be a form of concealment (ستر) or not?

The questioner's request for reassurance through a virginity test is not possible, because the presence of virginity does not necessarily indicate a girl's chastity, and she may lose it for reasons other than intercourse. Therefore, unveiling the 'awrah — especially the grave 'awrah — is not considered a permissible necessity in this case, and the prohibition of unveiling it remains as per the original ruling.