@Override
  protected Directory getDirectory(Path path) throws IOException {
    final FileSystemStats stats = mock(FileSystemStats.class);

    // This is super lame, but log4j automatically sets the system property, and the lucene
    // test asserts that no system properties have changed. Unfortunately, there is no
    // way to control the order of rules, so we can't clear this property with a rule
    // or @After method. Instead, do it in the close method of the directory.
    return new RegionDirectory(new ConcurrentHashMap(), stats);
  }
A unit test of the RegionDirectory class that uses the Directory test case from the lucene code
base.

This test is still mocking out the underlying cache, rather than using a real region.
geode-lucene/src/test/java/org/apache/geode/cache/lucene/internal/directory/RegionDirectoryJUnitTest.java