Make the error message explicit.

dito

Please add test for large numbers.

dito

Please make the refactoring in a different diff.

I think you should create a function to check for div and mod taking 4 paremeter: arguement's a and b passed to the ops, result of div and result of mod.

Then you can check all kind of properties, such as -a/b = -div, a/-b = -div and so on. This allows you to have many more test cases and grill the opcodes behavior.

Please put comments on the line before the code it refers to rather than on the same line.

If you create the function i u=suggested earlier, you'd have all these types of test case taken care of automagically.

This won't handle zero properly. An empty valtype should return a valtype with {0x80} when negated.

This also calls for a test for NegativeValtype.

I think you should really have one check function that take result for div and mod. This ensure by design that you all test cases for both. It's not a big deal to have too many tests cases for one or the other.

You don't need to say valtype everywhere if you put the function call on the left.

You don't need to specify stacktype all over the place.

Why no CheckDivMod ?

Known results, such as a/a = 1 and a/1 = a and can also be added to CheckDivMod so they get grilled with many values of a.

Put positive and negative zeros in there.

This is also a property that can be checked by CheckDivMod on many values.

You are missing the minimally encoded zero: {}

You should have a CheckDivModError as these error should happen for both div and mod.

dito

This would become redundant

This would become redundant as well.

And this can be merged in div_and_mod_opcode_tests