ok here's a few tests. none of them by themselves is conclusive about quality and none of them when failed by themselves mean bad hash
, but all together give a good idea of whether its good hash:
When putting a lighter next to it, it should bubble, and not just turn black. it should not be too hard and neither too soft at room temperature. If its hard, getting a piece and playing around with it in your hand, pressing and so on should make it more maleable.
When it becomes maleable with a little heat from hand or passing the lighter quickly a few times, one should be able to roll it into a ball with a smooth surface
it generally should be lighter colour in the middle than on the outside. When one warms it up, it should get darker.
the most common type of hash is morrocan. It goes from light brown to dark brown. Charas has a greener tint to the colour, and may be more black-ish also.
with the best quality, one should be able to roll a little snake out of the hash and light it up. The amber should keep lighten by itself for at least a little while.
and.. it should make one stoned