@Test
  public void testFileSystemWithDefaultWatchService() throws IOException {
    FileSystem fs = Jimfs.newFileSystem(Configuration.unix());

    WatchService watchService = fs.newWatchService();
    assertThat(watchService).isInstanceOf(PollingWatchService.class);

    PollingWatchService pollingWatchService = (PollingWatchService) watchService;
    assertThat(pollingWatchService.interval).isEqualTo(5);
    assertThat(pollingWatchService.timeUnit).isEqualTo(SECONDS);
  }
Tests for {@link Configuration}, {@link Configuration.Builder} and file systems created from
them.

@author Colin Decker
jimfs/src/test/java/com/google/common/jimfs/ConfigurationTest.java