public void OnWritingSystemIDChange_DifferentId_OldIdIsRemoved()
        {
            var ws = new WritingSystemDefinition("fr");

            RepositoryUnderTest.Set(ws);
            Assert.IsTrue(RepositoryUnderTest.Contains("fr"));
            ws.Language = "th";
            RepositoryUnderTest.OnWritingSystemIDChange(ws, "fr");
            Assert.IsFalse(RepositoryUnderTest.Contains("fr"));
            Assert.IsTrue(RepositoryUnderTest.Contains("th"));
        }