If you have a good answer to that, then the lexer is separate (as others said). If you don't then wirte parser tests for the lexer so that you can more easily refractor the interface between them.
There is no on right answer, only trade-offs. You need to make the right decision for you. (though I will note that there is probably a good reason parse and lex are generally separated and that probably means that the best tradeoffs for you is they are separate. But if you decide different you are not necessarily wrong)
If you have a good answer to that, then the lexer is separate (as others said). If you don't then wirte parser tests for the lexer so that you can more easily refractor the interface between them.
There is no on right answer, only trade-offs. You need to make the right decision for you. (though I will note that there is probably a good reason parse and lex are generally separated and that probably means that the best tradeoffs for you is they are separate. But if you decide different you are not necessarily wrong)