public Map<String, Object> originalsWithPrefix(String prefix) {
        return originalsWithPrefix(prefix, true);
    }
@Test
    public void testOriginalsWithPrefix() {
        Properties props = new Properties();
        props.put("foo.bar", "abc");
        props.put("setting", "def");
        TestConfig config = new TestConfig(props);
        Map<String, Object> originalsWithPrefix = config.originalsWithPrefix("foo.");

        assertTrue(config.unused().contains("foo.bar"));
        originalsWithPrefix.get("bar");
        assertFalse(config.unused().contains("foo.bar"));

        Map<String, Object> expected = new HashMap<>();
        expected.put("bar", "abc");
        assertEquals(expected, originalsWithPrefix);
    }