Why there are 2 variables called restState?

Please assert their values after call.

Those variables are restrictions for strtok_r to do thread-safe tokenization and to don't mix up tokenizations between two elements similar to themselves. Asserting this value is pointless because it is possible to assert this as not null, but we discard this option using the next tokenization without a mixup.

You can certainly add more cases to cover this funciton. First example would be strbrk("abc", "") For example:

• passing bytes in the s2 in various order, so strpbrk("abcde", "dce")
• passing more bytes (than available in s1) in s2, so sth like: strpbrk("abcde", "cdefgh")
• big buffers
• a few same bytes in s2
• maybe some other cases

I tried different approaches in those cases, I will wait for a response about them.

We can remove those local variables. As I mentioned before empty and "" are bot han empty string, so we can use only "".

I applied those changes, but in suggestions is an error because, with the string passed by hand, we can't assert PTR and one line above instead of passing string as "" i was forced to use "\0" (it resolve this problem) because of restrictions in variables passed to strtok(GCC)

oh, ok there is restrict in the declaration. Using "\0" seems to be fine in this case.

I don't quite understand, first call puts a NULL pointer in asciiStr[2], so each of next calls will return only "1" as a token, I don't see a purpose of asserting it 255 times.

I suppose you wanted to test mainly the rest there, which in fact is the same for all iterations (I don't see why only two of the last rests have to be equal)

We could also create a case, where the separator string contains the same character a few times, same with str, it could contain the same characters multiple times. There is no big case, we can do it at once in such one.

create a case, where the separator string contains the same character a few times

Where is such case? I can't see it for strtok() function.

Those cases are checked in multi_call in strtok and strtok_r

create a case, where the separator string contains the same character a few times

Where is such case? I can't see it for strtok() function.