public void TestGetAllFollowing() { IEnumerable <User> ienumableUsers = new List <User>() { user, userSecond }; mockFollowRepository.Setup(x => x.GetAllFollowing(It.IsAny <string>())).Returns(ienumableUsers); var followService = new FollowService(mockFollowRepository.Object); IEnumerable <User> getAllFollowing = followService.GetAllFollowing("5d111299f3b75e0001f4ed78"); User userActual = getAllFollowing.FirstOrDefault(); Assert.AreEqual(userActual, user); }