### Question:
Acl { public Set<Principal> getOwners() { return getClonedCopy(owners, ImmutableSet.toImmutableSet()); } 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 testGetOwners() { Acl acl = new Acl.Builder() .setReaders(user("AllowedUser1", "AllowedUser2")) .setDeniedReaders(group("DeniedGroup")) .setOwners(user("AllowedUser1")) .build(); assertEquals(user("AllowedUser1"), acl.getOwners()); ItemAcl itemAcl = acl.applyTo(new Item()).getAcl(); itemAcl.getOwners().remove(0); acl.getOwners().iterator().next().setUserResourceName("AllowedUser3"); assertEquals(user("AllowedUser1"), acl.getOwners()); thrown.expect(UnsupportedOperationException.class); acl.getOwners().addAll(group("AllowedGroup")); }