### Question:
ConfigSources { public static SystemPropertiesConfigSource.Builder systemProperties() { return new SystemPropertiesConfigSource.Builder() .properties(System.getProperties()); } private  ConfigSources(); static ConfigSource empty(); static ConfigSource create(Config config); static NodeConfigSource create(ConfigNode.ObjectNode objectNode); static ConfigSource create(InputStream data, String mediaType); static ConfigSource create(String content, String mediaType); static MapConfigSource.Builder create(Map<String, String> map); static MapConfigSource.Builder create(Map<String, String> map, String name); static MapConfigSource.Builder create(Properties properties); static MapConfigSource.Builder create(Properties properties, String name); static ConfigSource prefixed(String key, Supplier<? extends ConfigSource> sourceSupplier); static SystemPropertiesConfigSource.Builder systemProperties(); static MapConfigSource environmentVariables(); static ClasspathConfigSource.Builder classpath(String resource); static List<UrlConfigSource.Builder> classpathAll(String resource); static FileConfigSource.Builder file(String path); static FileConfigSource.Builder file(Path path); static DirectoryConfigSource.Builder directory(String path); static UrlConfigSource.Builder url(URL url);  }### Answer:
@Test public void testSystemPropertiesSourceType() { ConfigSource source = ConfigSources.systemProperties().build(); assertThat(source, is(instanceOf(ConfigSources.SystemPropertiesConfigSource.class))); assertThat(source.description(), is("SystemPropertiesConfig[]")); }