The test using \removepunctuation that you provided does what it should be doing (it produces 6 instances of "test-test" with the intervening punctuation mark in each case removed), but it doesn't do what I'm trying to do in the MWE above. I'm trying to take certain punctuation marks that follow the \autopuncttest macro and place them before it instead. Looking at the typo-chr .lua and .mkiv files, I see that there are \pushpunctuation and \poppunctuation methods in addition to the \removepunctuation method. These might be useful for this purpose, but in any case, I still have to check if the trailing character is one of the characters in a specified set/string, and this is where the error is arising.