When building on windows, the quick.html will have different line endings after checkout from GIT. The test will then fail because of difference between actual length of quick.html test file and expected length of quick.html attachment in quick-winmail.dat file.
The master copy of our source control is current SVN - https://svn.apache.org/repos/asf/poi/trunk/ . I believe we have appropriate line endings set on the file, but I'm not sure. Could you try with a svn checkout, and let us know if it's a general Windows issue, or just a problem with the SVN to Git sync?
I checked with the svn checkout. In svn, the file is correctly set with a property to leave the EOL "as-is". So, this seems to be a problem of the git bridge on github. Maybe a hint on the build-with-git part of the website would be helpful, that this test might fail because of the checkout issue.
Let's keep it open to check if adding a .gitattribute file can solve this.
Based on https://help.github.com/articles/dealing-with-line-endings/ and https://stackoverflow.com/questions/2517190/how-do-i-force-git-to-use-lf-instead-of-crlf-under-windows it doesn't look like Git supports it on a file-by-file basis the same way SVN does. However, assuming we've been consistent everywhere, it looks like a .gitattributes file may let us get something close
We added a .gitattribute file with r1819771 that should make the file use just lf always.