@Test
  public void testCheckOpen() throws IOException {
    state.checkOpen(); // does not throw
    state.close();
    try {
      state.checkOpen();
      fail();
    } catch (ClosedFileSystemException expected) {
    }
  }
Tests for {@link FileSystemState}.

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