What is the optimal number of tests to screen a new hire & what types identify someone who will fit

One test plus one portfolio example for a tech applicant or one reference for a non-tech applicant.

I'm not an expert but I use time and intensity instead of quantity. How long can someone stay focused in front of the computer? Is this something I want to test for? Is it a technical test, English test, etc? Imho, these are "better" questions to ask instead of "how many". For my purposes, 25 minutes works best for me.