private void cleanDirectory(File tempDir) {
    File[] files = tempDir.listFiles();
    if (files != null) {
      for (File file : files) {
        assertTrue("The file [" + file.getAbsolutePath() + "] could not be deleted", file.delete());
      }
    }
  }
Deletes all the files in {@code tempDir}.
@param tempDir the directory whose files have to be deleted.
ambry-store/src/test/java/com/github/ambry/store/LogTest.java