private static FileChannel channel(RegularFile file, OpenOption... options) throws IOException {
    return new JimfsFileChannel(
        file,
        Options.getOptionsForChannel(ImmutableSet.copyOf(options)),
        new FileSystemState(new FakeFileTimeSource(), Runnables.doNothing()));
  }
Most of the behavior of {@link JimfsFileChannel} is handled by the {@link RegularFile}
implementations, so the thorough tests of that are in {@link RegularFileTest}. This mostly tests
interactions with the file and channel positions.

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