Diagnosis?
How many of you have been through a mental evaluation?
You can't "measure" some magical indicator, right? An opinion is made based on a series of questions basically. If someone wanted to hide their true feelings, be they depression, mania, psychosis... whatever, they easily can.
Only people who "want" to be helped will answer truthfully. When your job is on the line that isn't likely to happen is it?
I fear all this claptrap talk of "testing" has imaginary outcomes that reveals the "truth". Sadly that's not how it works. Sorry, but that's reality.