### Question:
SimpleGroup extends SimplePrincipal implements GroupPrincipal { public boolean isMember(Principal p) { return members.contains(p); } SimpleGroup(String groupName);  SimpleGroup(String groupName, String memberName);  SimpleGroup(String groupName, Principal member); boolean isMember(Principal p); boolean addMember(Principal p); Enumeration<? extends Principal> members(); boolean removeMember(Principal p); boolean equals(Object obj); int hashCode();  }### Answer:
@Test public void testIsMember() { assertTrue(new SimpleGroup("group", "friend").isMember(new SimplePrincipal("friend"))); assertFalse(new SimpleGroup("group", "friend").isMember(new SimplePrincipal("frogs"))); }