Currently, running prove with TAP::Formatter::JUnit supports an environment variable PERL_TEST_HARNESS_DUMP_TAP that sets a path where a directory t/ will be created, and for each test file x, new files named x and x.junit.xml are created in the directory. I would like to be able to format the output filenames in a different way. Is there any way to do this?
A quick look at TAP::Formatter::JUnit::Session says "no" - there is no way to modify it without writing your own formatter, deriving off TAP::Formatter::JUnit and overriding its open_test method to point to your own session, which would, in turn, be derived off TAP::Formatter::JUnit::Session with its dump_junit_xml overridden to do what you want - but now you're modifying the entire dump (and thus don't need to rely on that environment variable if you prefer).
I guess all that derivation is a way, though probably not the way you thought/were hoping.