public void testAddMemberToDeletedGroup() throws Exception
    {
        // Setup test fixture
        final String GROUP_NAME = "Test Group A";
        final GroupManager groupManager = GroupManager.getInstance();
        final Group group = groupManager.createGroup(GROUP_NAME);
        groupManager.deleteGroup(group);

        // Execute system under test.
        group.getMembers().add(new JID("test@example.org"));

        // Verify results.
        assertThrows(GroupNotFoundException.class, ()-> groupManager.getGroup(GROUP_NAME));
    }
Reproduces an issue where adding a member to a group that does not exist would cause the group to be added
to a cache, making it appear that this group exists.

@see <a href="https://igniterealtime.atlassian.net/browse/OF-2426">Group cache can contain ghost entries</a>
xmppserver/src/test/java/org/jivesoftware/openfire/group/GroupManagerNoMockTest.java