assertTrue(spy.flushed);
    assertFalse(spy.closed);

    writer.close();
    assertTrue(spy.flushed);
    assertTrue(spy.closed);
  }

  public void testCloseIsFinal() throws IOException {
    StringBuilder builder = new StringBuilder();
    Writer writer = new AppendableWriter(builder);

    writer.write("Hi");
    writer.close();

    assertThrows(IOException.class, () -> writer.write(" Greg"));