public String documentationOf(String key) {
        ConfigDef.ConfigKey configKey = definition.configKeys().get(key);
        if (configKey == null)
            return null;
        return configKey.documentation;
    }
@Test
    public void testDocumentationOf() {
        Properties props = new Properties();
        TestIndirectConfigResolution config = new TestIndirectConfigResolution(props);

        assertEquals(
                TestIndirectConfigResolution.INDIRECT_CONFIGS_DOC,
                    config.documentationOf(TestIndirectConfigResolution.INDIRECT_CONFIGS)
        );
    }