@Test
  public void testClose_multipleTimesDoNothing() throws IOException {
    state.close();
    assertEquals(1, onClose.runCount);
    state.close();
    state.close();
    assertEquals(1, onClose.runCount);
  }
Tests for {@link FileSystemState}.

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