@Test
  public void testAsyncChannel() throws Throwable {
    RegularFile file = regularFile(15);
    ExecutorService executor = Executors.newSingleThreadExecutor();
    JimfsAsynchronousFileChannel channel = channel(file, executor, READ, WRITE);

    try {
      assertEquals(15, channel.size());

      assertSame(channel, channel.truncate(5));
      assertEquals(5, channel.size());

      file.write(5, new byte[5], 0, 5);
      checkAsyncRead(channel);
      checkAsyncWrite(channel);
      checkAsyncLock(channel);

      channel.close();
      assertFalse(channel.isOpen());
    } finally {
      executor.shutdown();
    }
  }
Just tests the main read/write methods... the methods all delegate to the non-async channel
anyway.
jimfs/src/test/java/com/google/common/jimfs/JimfsAsynchronousFileChannelTest.java