(which is good: our tests have intentional violations), but
                     Error Prone doesn't know it's building test code unless we
                     pass -XepCompilingTestOnlyCode, and that argument needs to
                     be passed as part of the same <arg> as -Xplugin:ErrorProne,
                     and I gave up trying to figure out how to do that for test

            won't.

            I have one idea for a better approach, but it's painful, and I haven't tested it: We
            could postprocess Collect.gwt.xml to add <skip> lines for all the files that should be
            covered by testModule.gwt.xml. Maybe I'll try it someday.

            [*] https://code.google.com/p/google-web-toolkit/wiki/ResourceOracle#When_multiple_PathPrefix_es_have_the_same_path