final LineFileDocs docs = new LineFileDocs(random, defaultCodecSupportsDocValues());
final File tempDir = _TestUtil.getTempDir(testName);
dir = newMockFSDirectory(tempDir); // some subclasses rely on this being MDW
dir.setCheckIndexOnClose(false); // don't double-checkIndex, we do it ourselves.
final IndexWriterConfig conf = newIndexWriterConfig(TEST_VERSION_CURRENT,
new MockAnalyzer(random())).setInfoStream(new FailOnNonBulkMergesInfoStream());
if (LuceneTestCase.TEST_NIGHTLY) {
// newIWConfig makes smallish max seg size, which
// results in tons and tons of segments for this test
// when run nightly: