OOh thata REALLY bad repair job!
Method for hardness testing:
First, the head needs to clean. No carbon, oil or sand-blasting residue on the faces to be tested.
There are a variety of tools that are used to test haardness, ranging from a fully electronic device to a calebrated hollow tube with a ball bearing in it.
They all work by dropping a ball bearing onto the surface and measuring the rebound.
Making sure that the tool is flat on the face of the head, test the head in about six or seven places. Include between the cylinders (not on any badly sunken gasket marks), above the exhaust port on the face, above the inlet port and on the rocker gasket rail as well.
Generally the higher the average the better but stats are about 65 Brinell as a throw away mark for any low result to about a 75 average min. The higher the average, the happier the head.
Nev, ALL cylinder heads should be pressure tested as a process of reconditioning - most preferably with a very hot photofloresent fluid. That way a black light will show any hairline cracks that would not normally be picked up.