[[Module:ny-IPA]]

Could you help me with this? I don't really understand the rules for the testcases that are currently failing.

Where are the testcases?

Module:ny-IPA/testcases.

Just a hunch but, did you normalise the text to NFC before returning it? This combines diacritics with the characters before them, when possible. I found that while MediaWiki does this to the page content when you save a page, Lua doesn't do it.

Actually, never mind that. I see the problems. There's ˈ expected but .ˈ in the output.

That's not the only problem, though.