@feruze - I don't think that face validity is as important as getting statistical data and evidence to back up what you are doing.
What if you are questioned about the validity of your test by an official agency after you use the test? You can't say, "oh my colleagues said that it is a valid test." You have to have proof. You have to have statistical proof and you have to have content validity from experts of that subject about the method you used and how you prepared and carried out the test or experiment.