how to Mock Entity Framework DbContext for Unit Testing Repository Methods Using Moq
I'm trying to configure I'm learning this framework and I've encountered a strange issue with Does anyone know how to I'm following best practices but I'm trying to unit test my repository methods that interact with Entity Framework's `DbContext`, but I'm running into issues with setting up my mocks using Moq. My repository looks something like this: ```csharp public class UserRepository : IUserRepository { private readonly AppDbContext _context; public UserRepository(AppDbContext context) { _context = context; } public User GetUserById(int id) { return _context.Users.Find(id); } } ``` In my test class, I want to mock `AppDbContext` to avoid hitting the actual database. However, when I set up my mock and try to call `GetUserById`, I'm getting a `NullReferenceException` because the `Users` property on `_context` is null. Here's how I'm currently trying to set up my test: ```csharp public class UserRepositoryTests { [Fact] public void GetUserById_ReturnsUser_WhenUserExists() { // Arrange var mockSet = new Mock<DbSet<User>>(); var mockContext = new Mock<AppDbContext>(); mockContext.Setup(m => m.Users).Returns(mockSet.Object); var userRepo = new UserRepository(mockContext.Object); // Act var user = userRepo.GetUserById(1); // Assert Assert.NotNull(user); } } ``` I've tried setting up `mockSet` to return a list of users using `mockSet.As<IQueryable<User>>().Setup(...)`, but it seems like the method doesn't know how to resolve that query. Here's the specific behavior I'm working with: ``` Object reference not set to an instance of an object. ``` I've also tried using InMemory Database from EF Core, but I wanted to avoid that to keep my tests fast and isolated. Is there a better way to mock the `DbContext` and its `DbSet` properties to avoid these issues? Any insights would be appreciated! Any pointers in the right direction? Am I missing something obvious? The stack includes C# and several other technologies. Could someone point me to the right documentation? What am I doing wrong? I'm working in a macOS environment. This issue appeared after updating to C# 3.9. I appreciate any insights!