public async Task InvitePlayer_ThatHasAlreadySigned()
        {
            var clan = await _handler.CreateClan("egal", "CS", "Peter#123");

            await _handler.InviteToClan("NewGUY#123", clan.ClanId, "Peter#123");

            await _handler.AcceptInvite("NewGUY#123", clan.ClanId);

            Assert.ThrowsAsync <ValidationException>(async() => await _handler.InviteToClan("NewGUY#123", clan.ClanId, "Peter#123"));
        }