How do u do unit test?

my idea including:
build test map, then get standard things, screenshot, culling result, hdr value,memory, time and so on
we can update these, and store them;
when we update code, we check for the difference;
the result includes,if it's different, how much it's different, need we update the standard things;
keep on do this, so we can code and feel pretty reassuring;

It's very hard to unit test rendering operations. What you can do (if culling happens to take place on software) is to verify known corner cases with unit tests:

* input set contain A,B,C,D
* run culling on this set
* output set should contain A,B,D

If culling takes place on the hardware, it's going to be far less easy. Verifying reference images doesn't help much in this case (image comparison is quite difficult).

Remember that unit test should try to test simple things. The more complex the operation is, the more corner cases you'll have, and the more difficult it will be to correctly test the product. Unit testing complex systems is not only very hard, it's only not that useful - because two different problems can produce a correct output for most cases, so getting the diagnostic right is going to be harder.

Regards,