public void AddMemberToTeam() { // Arrange var teams = new List <Team>() { new Team(), new Team(), new Team() }; _context.Teams.AddRange(teams); _context.SaveChanges(); var players = new List <Player>() { new Player(), new Player(), new Player() }; // Act _target.AddMemberToTeam(teams[1], players); // Assert Check.That(teams[1].Players).ContainsExactly(players); Check.That(_context.Players).ContainsExactly(players); }