for prod and one for tests. However, unlike our other packages, as of this
    writing it has test supersource but no prod supersource.

    GWT happens to use the prod .gwt.xml, so it looks for no supersource for
    tests, either. This causes it to fail to find AtomicLongMapTest.

    Our workaround is to tell GWT that util.concurrent and all other packages
    have prod supersource, even if they have none. GWT is happy to ignore us

    for prod and one for tests. However, unlike our other packages, as of this
    writing it has test supersource but no prod supersource.

    GWT happens to use the prod .gwt.xml, so it looks for no supersource for
    tests, either. This causes it to fail to find AtomicLongMapTest.

    Our workaround is to tell GWT that util.concurrent and all other packages
    have prod supersource, even if they have none. GWT is happy to ignore us

              <!-- FeatureUtilTest.*ExampleDerivedInterfaceTester, com.google.common.io.*Tester, incidentally FeatureSpecificTestSuiteBuilderTest.MyAbstractTester (but we don't care either way because it's not meant to run on its own but works OK if it does)... but not NullPointerTesterTest, etc. -->
              <exclude>%regex[.*Tester.class]</exclude>
              <!-- Anonymous TestCase subclasses in GeneratedMonitorTest -->

            like to get an error. Currently we do, but if we add the extra <inherits> lines, we
            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.