@Test
public void shouldReadStringValue() {

    List<String> list = new ArrayList<>();
    observer.onStringValue("prop", "foo,bar", str -> {
        list.clear();
        list.add(str);
    });
    assertThat(list).containsOnly("foo,bar");
    writeConfigLine("prop=a,  b ,c");
    assertThat(list).containsOnly("a,  b ,c");
}