public String asString() {
        return this.stream().map(ConfigErrors::asString).collect(Collectors.joining(", "));
    }
@Test
    public void shouldGetAConsolidatedListOfErrorsAsMessage() {
        AllConfigErrors errors = new AllConfigErrors();
        errors.add(error("key1"));
        errors.add(error("key2"));
        errors.add(error("key3"));
        assertThat(errors.asString(), is("error on key1, error on key2, error on key3"));
    }