Produce test failure if some tests cannot be executed due to lacking data
In some cases, some files (such as Unicode data files) may be missing and cannot be downloaded.
In these cases, tests should not fail silently. It is not good to produce a long list of test failures when there is only a single problem. Therefore, e.g. test/ruby/enc/test_case_comprehensive.rb up to r55520 produced a single explicit failure when tests were missing.
In revision r55521, this test was removed, but it should be reinstated to avoid silent failure.