String { public List<String> getString() { if (string == null) { string = new ArrayList<>(); } return string; }  List<String> getString();  }
@Test public void getStrings() throws Exception { String initialString = new String(); List<String> strings = asList(initialString); String string = stringBuilder().string(strings); assertThat(string.getString().size(), is(1)); assertThat(string.getString().get(0), is(initialString)); }