There are preliminary non-destructive test, Thumb Pad Test, Arm Hair Test, and Visual test.

TPT takes time to learn,

AHT is not always conclusive many factor are involved and

Visual Magnification, also takes experience to learn what to look for, but is fairly conclusive.

The only real test and the definitive test is… the shave. It will shave or it won’t.

So the real answer is, you do all three… then shave.

Now, you just need to learn to shave and maintain your razor.