sink.writeLines(ImmutableList.of("foo", "bar", "baz"), "\n");
    assertEquals("foo\nbar\nbaz\n", sink.getString());
  }

  public void testWriteLines_withDefaultSeparator() throws IOException {
    sink.writeLines(ImmutableList.of("foo", "bar", "baz"));
    String separator = System.getProperty("line.separator");