}

    @Test
    public void test_jsonFormatter_fileExtension() {
        final JsonIndexExportFormatter formatter = new JsonIndexExportFormatter();
        assertEquals(".json", formatter.getFileExtension());
        assertEquals("index.json", formatter.getIndexFileName());
    }

    @Test
    public void test_jsonFormatter_emptyCollection() {
        final Map<String, Object> source = new LinkedHashMap<>();