public void test_convertWithNumbers() {
        List<String> results = converter.convert("テスト123", null);
        assertNotNull(results);
        assertTrue(results.size() > 0);
    }

    public void test_convertLowercase() {
        // All results should be lowercase
        List<String> results = converter.convert("アイウ", null);
        for (String result : results) {
            assertEquals(result, result.toLowerCase());