### Question:
Acl { public static boolean addResourcePrefixGroup(Principal group, String identitySourceId) { checkNotNull(group); String groupName = group.getGroupResourceName(); checkArgument(!Strings.isNullOrEmpty(groupName), "groupName can not be empty or null"); if (groupName.startsWith(IDENTITY_SOURCES_PREFIX)) { return false; } group.setGroupResourceName(String.format(GROUP_NAME_FORMAT, identitySourceId, groupName)); return true; } private  Acl(Builder builder); Set<Principal> getReaders(); Set<Principal> getDeniedReaders(); Set<Principal> getOwners(); String getInheritFrom(); String getInheritFromFragment(); InheritanceType getInheritanceType(); Item createFragmentItemOf(String id, String fragment); Item applyTo(Item item); static String fragmentId(String id, String fragment); static String getPrincipalName(String name, String namespace); static Principal getGoogleUserPrincipal(String userId); static Principal getGoogleGroupPrincipal(String groupId); static Principal getCustomerPrincipal(); static Principal getUserPrincipal(String userId); static Principal getUserPrincipal(String userId, String identitySourceId); static Principal getGroupPrincipal(String groupId); static Principal getGroupPrincipal(String groupId, String identitySourceId); static boolean addResourcePrefixUser(Principal user, String identitySourceId); static boolean addResourcePrefixGroup(Principal group, String identitySourceId); static PrincipalType getPrincipalType(Principal p); static Acl createAcl(String permittedUsers, String permittedGroups, String deniedUsers,
      String deniedGroups); @Override int hashCode(); @Override boolean equals(Object obj); @Override String toString(); static final String IDENTITY_SOURCES_PREFIX; static final String IDENTITY_RESOURCE_NAME_FORMAT; static final String USER_RESOURCE_NAME_FORMAT; static final String GROUP_NAME_FORMAT; static final UserPrincipalParser USER_PARSER; static final GroupPrincipalParser GROUP_PARSER; static final String GOOGLE_ACCOUNT_PREFIX; }### Answer:
@Test public void addResourcePrefixGroup() { Principal principal = Acl.getGroupPrincipal("john doe"); String before = principal.toString(); assertTrue(before, Acl.addResourcePrefixGroup(principal, "foo")); String after = principal.toString(); assertThat(after, not(equalTo(before))); assertFalse(after, Acl.addResourcePrefixGroup(principal, "foo")); assertEquals(after, principal.toString()); }