I think it's great to have unit testing confirm the entire message, just to validate that it looks reasonable and is properly constructed rather than just "somewhere in the string is the word 'parsing' and somewhere is the bad string". But you're verifying the core error condition and the expected identifying name/string, so I'll stop beating you up about style details. Good.

I mainly don't want a minor change to the error message to break all of the relevant test cases. This should be enough validation to ensure that all required info is present.