private static void checkAsyncWrite(AsynchronousFileChannel asyncChannel) throws Throwable {
    ByteBuffer buf = buffer("1234567890");
    assertEquals(10, (int) asyncChannel.write(buf, 0).get());

    buf.flip();
    SettableFuture<Integer> future = SettableFuture.create();
    asyncChannel.write(buf, 0, null, setFuture(future));

    assertThat(future.get(10, SECONDS)).isEqualTo(10);
  }
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