settings.addProxy(proxy1);

        SimpleProblemCollector problems = new SimpleProblemCollector();
        validator.validate(settings, problems);
        assertEquals(1, problems.messages.size());
        assertContains(problems.messages.get(0), "'proxies.proxy.host' for default is missing");
    }

    private static class SimpleProblemCollector implements SettingsProblemCollector {