assertTrue(results.contains("fyu"));
        assertFalse("Should not contain 'hyu' (that's for ヒュ)", results.contains("hyu"));
    }

    public void test_convertEmptyString() {
        List<String> results = converter.convert("", null);
        assertNotNull(results);
        assertTrue(results.size() > 0);
    }

    public void test_convertMixedText() {