I sketched the following:

class ModuleDescriptor_Test {

  @Test
  void test() {
    // GIVEN
    Module underTest = ModuleLayer.boot().findModule("org.assertj.core").orElseThrow();
    // WHEN
    Set<String> packages = underTest.getPackages().stream().filter(p -> !p.contains("internal")).collect(toSet());
    // THEN
    then(packages).allMatch(underTest::isExported);
  }

}

It can be executed on main as module descriptors are handled appropriately, but we don't have a chance on 3.x as everything runs on the classpath and findModule("org.assertj.core") returns an empty optional.

I'm going ahead with the merge and will add the test above on main only, so that we can spot such issues when forward-porting changes.

Thanks for your first contribution, @duponter!

You're welcome. But I should thank you for maintaining this fine library and the swift response to my bug ticket.