### Question:
User implements Serializable { public String getUsername() { return username; } User(String username); String getUsername(); void setUsername(String username); void listenToMessages(MessageReceivedObserver observer); void receiveMessage(Message message); @Override boolean equals(Object o); @Override int hashCode(); @Override String toString();  }### Answer:
@Test public void usernameTest() { assertEquals("john", john.getUsername()); }