> but one of them special-cases byte values using a lookup table generated from the other, you wouldn't expect mutation testing to catch the discrepancy
Sure you would. If the mutation tester mutates that lookup table. Which is quite easy to do, and which mutmut will do (if that lookup table is inside a function, because mutmut is based on mutant schemata).
If the mutation tester mutates that lookup table, then that will eventually lead to all entries in the lookup table being tested. That does not mean that the four divergent values outside the lookup table will end up being tested.
Sure you would. If the mutation tester mutates that lookup table. Which is quite easy to do, and which mutmut will do (if that lookup table is inside a function, because mutmut is based on mutant schemata).