### Question:
LogContext { public static void set( String key, String value ) { MDC.put(key, value); }  static void set( String key,
                            String value ); static String get( String key ); static void remove( String key ); static void clear();  }### Answer:
@Test public void shouldAcceptValidKeys() { LogContext.set("username", "jsmith"); logger.info(MockI18n.passthrough, "tracking activity for username"); logger.info(MockI18n.passthrough, "A second log message"); }