public void FindAllWritingSystemsWithData_FindsHiddenWritingSystems()
        {
            var wsMgr = Cache.ServiceLocator.WritingSystemManager;

            wsMgr.GetOrSet("en", out var en);
            wsMgr.GetOrSet("fr", out var fr);
            wsMgr.GetOrSet("fr-x-has-no-strings", out _);
            wsMgr.GetOrSet("fr-x-zero-length", out var zeroLength);
            wsMgr.GetOrSet("blz", out var blz);
            wsMgr.GetOrSet("hid", out var hid);
            wsMgr.GetOrSet("hid-x-embedded", out var hidEmbedded);
            wsMgr.GetOrSet("hid-x-edgeCase", out var hidEdgeCase);
            wsMgr.GetOrSet("hid-x-baselineText", out var hidBaseline);
            var entry = SenseOrEntryTests.CreateInterestingLexEntry(Cache);

            entry.CitationForm.set_String(hid.Handle, "Headword");
            entry.CitationForm.set_String(zeroLength.Handle, string.Empty);
            var exampleBldr = new TsStrBldr().Append("Example ", blz.Handle).Append("with embedded WS", hidEmbedded.Handle).Append("!", blz.Handle);
            var example     = Cache.ServiceLocator.GetInstance <ILexExampleSentenceFactory>().Create();

            entry.SensesOS.First().ExamplesOS.Add(example);
            // The Example MultiString has an Edge Case alternative, but no Edge Case text.
            example.Example.set_String(hidEdgeCase.Handle, exampleBldr.GetString());
            // Interlinear texts are monolingual strings.
            AddInterlinearTextToLangProj("Title").ContentsOA.AddNewTextPara(null).Contents = TsStringUtils.MakeString("Content", hidBaseline.Handle);

            // SUT
            var result = WritingSystemServices.FindAllWritingSystemsWithText(Cache);

            Assert.That(new SortedSet <int>(result), Is.EquivalentTo(new[]
            {
                en.Handle, fr.Handle, blz.Handle, hid.Handle, hidEmbedded.Handle, hidEdgeCase.Handle, hidBaseline.Handle
            }));
        }