source.forEachLine(builder::add);

    assertEquals(SPLIT_LINES, builder.build());
    assertTrue(source.wasStreamOpened());
    assertTrue(source.wasStreamClosed());
  }

  public void testCopyToAppendable_doesNotCloseIfWriter() throws IOException {
    TestWriter writer = new TestWriter();
    assertFalse(writer.closed());
    source.copyTo(writer);
    assertFalse(writer.closed());
  }