The JUnit Result Archiver will fail the build if the test result files that match the filemask do not have a very recent modification time. The error message it prints is this:
"Test reports were found but none of them are new. Did tests run?"
This can be inconvenient in several settings; notably, when the clocks on the master and slave fall out of sync, or when the test results were generated by some process that isn't part of the build itself – maybe they were scp'd from somewhere else, for instance. Or for testing the JUnitResultArchiver itself.
In my opinion, the behavior should be changed such that check-for-recent-modifications should be off by default. Additionally, the user should be able to specify a "recent" threshold via a setting.