How to mock UnitOfWork when using transactions (NUnit and NSubstitute) - unit-testing

Question

I have created a Web API using ASP.NET Core 3.1 and EF Core 5.0. Data is stored in a MSSQL database.
I have implemented UnitOfWork and repository pattern.
The UnitOfWork class has a method used to create transactions and it look like this:
//UnitOfWork
public async Task ExecuteTransaction(Func<Task> insideTransactionFunction)
{
var transaction = await _context.Database.BeginTransactionAsync();
try
{
await insideTransactionFunction();
await transaction.CommitAsync();
}
catch (Exception)
{
await transaction.RollbackAsync();
throw;
}
}
Im trying to write tests, for service classses that uses the UnitOfWork class to modify the data in the SQL database. Fx when adding a user using the UserService:
//UserService
public async Task<User> AddUserAsync(User user)
{
await _unitOfWork.ExecuteTransaction(async () =>
{
//Add user locally to generate the local id
_unitOfWork.UserRepository.Add(user);
await _unitOfWork.SaveChangesAsync();
//...Some logic that uses the generated user id...
if(string.IsNullOrWhiteSpace(email.User) == false)
{
//Inviting the user returns the generated Azure User id
user.AzureUserId = _azureService.InviteUser(user.Email);
await _unitOfWork.SaveChangesAsync();
}
}
return user;
}
A test for the above method could look like this:
//UserServiceTests
public async Task AddUserAsync_UserQualifiesForAzureInvite_AzureUserIdSetOnCreatedUser()
{
//Arrange
var unitOfWork = Substitute.For<IUnitOfWork>();
var azureService = Substitute.For<IAzureService>();
var uut = new UserService(unitOfWork, azureService);
var newUser = new User { ... some setup ... };
var azureUserId = Guid.NewGuid();
azureService.InviteUser(null).ReturnsForAnyArgs(Task.FromResult(azureUserId));
//Act
var createdUser = await _uut.AddUserAsync(newUser); //Returns right away
//Assert
Assert.That(createdUser.AzureUserId, Is.EqualTo(azureUserId));
}
The problem is that the transaction created with UnitOfWork is ignored and the user is returned straight away.
public async Task<User> AddUserAsync(User user)
{
//Skipped from here...
await _unitOfWork.ExecuteTransaction(async () =>
{
//
}
//...To here
return user;
}
So my question is: How can i mock the UnitOfWork class and still be able to test code wrapped in the the transaction?

Answer 1

My architecture was fundamentally flawed. Check out the comments and links made by Panagiotis Kanavos.
The solution was to get rid of UnitOfWork and the repositories and it seems testable now.