@Override
    public Appendable append(CharSequence csq) {
        try {
            return out.append(csq);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
@Test
    void append() {
        out.append("Hello");
        out.append("Hello World", 5, 11);
        out.close();
        assertThat(bytes, bytes(equalTo("Hello World")));
    }