private void createTestJarWithXml(File jarFile, String xmlContent) throws Exception {
        try (JarOutputStream jos = new JarOutputStream(new FileOutputStream(jarFile))) {
            JarEntry entry = new JarEntry("fess_ds++.xml");
            jos.putNextEntry(entry);
            jos.write(xmlContent.getBytes());
            jos.closeEntry();
        }
    }

    // Test DataStore implementation for testing

    Entry<String, Collection<Integer>> barEntry = entries.next();
    assertEquals("bar", barEntry.getKey());
    assertThat(barEntry.getValue()).containsExactly(1, 3).inOrder();
    assertThrows(
        UnsupportedOperationException.class, () -> barEntry.setValue(Arrays.<Integer>asList()));
    entries.remove(); // clear