Actually running mvn clean test passes for the main branch while it fails if your pull request is applied (see https://travis-ci.com/github/xmlunit/xmlunit/jobs/479835608 for example).

The test is not related to the line you mention, it verifies the error message created by AssertJ's AbstractCharSequenceAssert (it is what this class' isEqualTo creates as message) and thus may be sensitive to the version of AssertJ used as a dependency. If you've changed the AssertJ version used when building the module, this could explain the test failure on your side.

I think assertj/assertj@5ae16a9 is responsible for the test failure. It went into AssertJ 3.19.0.

The xmlunit-assertj module explicitly wants to support AssertJ 2.x and we encourage users to use xmlunit-assertj3 if they want to use AssertJ 3.x instead.

I see a couple of options:

1. you somehow manage to compile the different XMLUnit modules against different versions of AssertJ - this is what Maven does by default and why it works outside of your build environment.
2. you drop the xmlunit-assertj module (and potentially make your users unhappy)
3. we rewrite the test assertion so it works with both AssertJ 2.x and AssertJ 3.19.0+

most likely we'll end up with the last option but maybe I'm overlooking something. If we want to allow either message pattern, we should do so as strictly as possible. A test that only looked for the presense of substrings would miss bugs like #210.

please take a look at https://github.com/xmlunit/xmlunit/compare/212-prototype?expand=1 - if this works for you, I'll expand it to the assertj3 module and add a compat-test for AssertJ 3.19.0

@bodewig Thanks for the feedback and improved patch! I checked your proposed patch with a Fedora build and it almost works. The %n references in the AssertJ 3.19.0+ pattern alternative simply need to be changed to \n and it's good.

thanks. If you were building XMLUnit 2.8.x you'd get related issues for the xmlunit-assertj3 module, it looks as if I needed to adjust more patterns there.

@bodewig I just updated this PR with the improved patch. The package in Fedora is still using 2.7.0, and this patch is sufficient for that. Thanks again!

Coverage remained the same at 91.948% when pulling 87796e0 on mmathesius:exception-format-update into 5b66f10 on xmlunit:main.

Many thanks