Light.DataAccessMocks

This library provides mocks for the data access abstractions of Light.SharedCore that you can use in your unit tests.

How to install

Light.DataAccessMocks is compiled against .NET Standard 2.0 and 2.1 and thus supports all major platforms like .NET and .NET Framework, Mono, Xamarin, UWP, or Unity.

Light.DataAccessMocks is available as a NuGet package and can be installed via:

Package Reference in csproj: <PackageReference Include="Light.DataAccessMocks" Version="2.0.0" />
dotnet CLI: dotnet add package Light.DataAccessMocks
Visual Studio Package Manager Console: Install-Package Light.DataAccessMocks

What does Light.DataAccessMocks offer you?

With Light.DataAccessMocks, you can easily create mock sessions for the data access abstractions of Light.SharedCore. This library provides base classes that allow you to easily check that a session was correctly disposed, that changes were saved, that transactions were committed, or that a session was never opened.

Mocking read-only sessions

Read-only sessions are those sessions that only read data from your source system, usually not requiring a transaction. You can derive from the AsyncReadOnlySessionMock or ReadOnlySessionMock to mock the IAsyncReadOnlySession or IReadOnlySession interfaces. The following example shows this for an asynchronous use case:

public interface IGetContactSession : IAsyncReadOnlySession
{
    Task<Contact?> GetContactAsync(int id);
}

Consider the following ASP.NET Core controller that uses this session:

[ApiController]
[Route("api/contacts")]
public sealed class GetContactController : ControllerBase
{
    public GetContactController(IAsyncFactory<IGetContactSession> sessionFactory) =>
        SessionFactory = sessionFactory;

    private IAsyncFactory<IGetContactSession> SessionFactory { get; }

    [HttpGet("{id}")]
    public async Task<ActionResult<Contact>> GetContact(int id)
    {
        if (id < 1)
        {
            ModelState.AddModelError("id", "The id must at least be 1");
            return ValidationProblem();
        }

        await using var session = await SessionFactory.CreateAsync();
        var contact = await session.GetContactAsync(id);
        if (contact == null)
            return NotFound();
        return contact;
    }
}

You could then test your controller with the following code in xunit:

public sealed class GetContactControllerTests
{
    public GetContactControllerTests()
    {
        Session = new GetContactSessionMock();
        SessionFactory = new AsyncFactoryMock<IGetContactSession>(Session);
        Controller = new GetContactController(SessionFactory);
    }

    private GetContactSessionMock Session { get; }
    private AsyncFactoryMock<IGetContactSession> SessionFactory { get; set; }
    private GetContactController Controller { get; }

    [Fact]
    public async Task MustReturnContactWhenIdIsValid()
    {
        Session.Contact = new Contact();

        var result = await Controller.GetContact(42);

        Assert.Equal(Session.Contact, result.Value);
        Session.MustBeDisposed(); // Use this to check if your controller properly disposed the session
    }

    [Fact]
    public async Task MustReturnNotFoundWhenIdIsNotExisting()
    {
        var result = await Controller.GetContact(13);

        Assert.IsType<NotFoundResult>(result.Result);
        Session.MustBeDisposed();
    }

    // AsyncReadOnlySessionMock automatically implements IAsyncReadOnlySession for you
    private sealed class GetContactSessionMock : AsyncReadOnlySessionMock, IGetContactSession
    {
        public Contact? Contact { get; set; }

        public Task<Contact?> GetContactAsync(int id) => Task.FromResult(Contact);
    }
}

In the above unit tests, the GetContactSessionMock derives from AsyncReadOnlySessionMock which automatically implements IAsyncReadOnlySession and tracks proper disposal of the session. You can use the MustBeDisposed method to check that the controller properly closed the session.

Mocking sessions

If your session manipulates data and thus implements IAsyncSession or ISession for transactional support, you can derive your mocks from the AsyncSessionMock or SessionMock base classes. The following example for updating an existing contact shows an asynchronous use case:

public interface IUpdateContactSession : IAsyncSession
{
    Task<Contact?> GetContactAsync(int id);
}

The controller that uses this session might look like this:

[ApiController]
[Route("api/contacts/update")]
public sealed class UpdateContactController : ControllerBase
{
    public UpdateContactController(IAsyncFactory<IUpdateContactSession> sessionFactory,
                                   UpdateContactDtoValidator validator)
    {
        SessionFactory = sessionFactory;
        Validator = validator;
    }

    private IAsyncFactory<IUpdateContactSession> SessionFactory { get; }
    private UpdateContactDtoValidator Validator { get; }

    [HttpPut]
    public async Task<IActionResult> UpdateContact(UpdateContactDto dto)
    {
        if (this.CheckForErrors(dto, Validator, out var badResult))
            return badResult;
        
        await using var session = await SessionFactory.CreateAsync();
        var contact = await session.GetContactAsync(dto.ContactId);
        if (contact == null)
            return NotFound();
        dto.UpdateContact(contact);
        await session.SaveChangesAsync();
        return NoContent();
    }
}

To test this controller, we might write the following unit tests in xunit:

public sealed class UpdateContactControllerTests
{
    public UpdateContactControllerTests()
    {
        Session = new UpdateContactSessionMock();
        SessionFactory = new AsyncFactoryMock<IUpdateContactSession>(Session);
        Controller = new UpdateContactController(SessionFactory, new UpdateContactDtoValidator());
    }

    private UpdateContactSessionMock Session { get; }
    private AsyncFactoryMock<IUpdateContactSession> SessionFactory { get; }
    private UpdateContactController Controller { get; }

    [Fact]
    public async Task UpdateEntityWhenIdIsValid()
    {
        var contact = new Contact { Id = 1, Name = "John Doe" };
        Session.Contact = contact;
        var dto = new UpdateContactDto(1, "Jane Doe");

        var result = await Controller.UpdateContact(dto);

        Assert.Equal("Jane Doe", contact.Name);
        Assert.IsType<NoContentResult>(result.Result);
        Session.SaveChangesMustHaveBeenCalled() // Use this method to ensure SaveChangesAsync was called
               .MustBeDisposed();
    }

    [Fact]
    public async Task RefuseUpdateWhenIdIsNonExisting()
    {
        var dto = new UpdateContactDto(42, "Buzz Greenfield");

        var result = await Controller.UpdateContact(dto);

        Assert.IsType<NotFoundResult>(result.Result);
        Session.SaveChangesMustNotHaveBeenCalled() // Use this method to ensure that SaveChangesAsync was NOT called
               .MustBeDisposed();
    }

    private sealed class UpdateContactSessionMock : AsyncSessionMock, IUpdateContactSession
    {
        public Contact? Contact { get; set; }

        public Task<Contact?> GetContactAsync(int id) => Task.FromResult(Contact);
    }
}

In the above unit test, UpdateContactSessionMock derives from AsyncSessionMock which implements IAsyncSession and tracks calls to SaveChangesAsync and DiposeAsync. The methods SaveChangesMustHaveBeenCalled and SaveChangesMustNotHaveBeenCalled are used to ensure that SaveChangesAsync is properly called by the UpdateContactController.

By the way, you can throw an arbitrary exception during SaveChanges by setting the ExceptionOnSaveChanges property.

Mocking transactional sessions

If you want to handle individual transactions in your code, you usually derive from the IAsyncTransactionalSession or ITransactionalSession interfaces.

public interface IUpdateProductsSession : IAsyncTransactionalSession
{
    Task<int> GetProductsCountAsync();

    Task<List<Product>> GetProductBatchAsync(int skip, int take);

    Task UpdateProductAsync(Product product);
}

This session might be used in a nightly job that update products for the next day:

public sealed class UpdateAllProductsJob
{
    public UpdateAllProductsJob(IAsyncFactory<IUpdateProductsSession> sessionFactory, ILogger logger)
    {
        SessionFactory = sessionFactory;
        Logger = logger;
    }
    
    private IAsyncFactory<IUpdateProductsSession> SessionFactory { get; }
    private ILogger Logger { get; }

    public async Task UpdateProductsAsync()
    {
        await using var session = await SessionFactory.CreateAsync();
        var numberOfProducts = await session.GetProductsCountAsync();
        const int batchSize = 100;
        var skip = 0;
        while (skip < numberOfProducts)
        {
            IAsyncTransaction? transaction = null;
            try
            {
                transaction = session.BeginTransactionAsync();
                var products = session.GetProductBatchAsync(skip, batchSize);
                foreach (var product in products)
                {
                    if (product.TryPerformDailyUpdate(Logger))
                        await session.UpdateProductAsync(product);
                }

                await transaction.CommitAsync();
            }
            catch (Exception exception)
            {
                Logger.Error(exception, "Batch {From} to {To} could not be updated properly", skip + 1, batchSize + skip);
            }
            finally
            {
                if (transaction != null)
                    await transaction.DisposeAsync();
            }

            skip += batchSize;
        }
    }
}

You can mock the session using the AsyncTransactionalSessionMock (or TransactionalSessionMock for synchronous scenarios). It implements the IAsyncTransactionalSession interface (or the ITransactionalSession interface, respectively) for you and tracks the transactions that are created and used:

public sealed class UpdateAllProductsJobTests
{
    public UpdateAllProductsJobTests(ITestOutputHelper output)
    {
        var logger = output.CreateTestLogger(); // This uses Serilog.Sinks.Xunit
        Session = new UpdateProductsSessionMock();
        var sessionFactory = new AsyncFactoryMock<IUpdateProductsSession>(Session);
        Job = new UpdateAllProductsJob(sessionFactory, logger);
    }

    private UpdateProductsSessionMock Session { get; }
    private UpdateAllProductsJob Job { get; }

    [Fact]
    public async Task AllTransactionsMustBeCommitted()
    {
        await Job.UpdateProductsAsync();

        Assert.Equal(5, Session.Transactions.Count);
        Session.AllTransactionsMustBeCommitted() // Use this method to ensure that all tracked transactions were committed
               .MustBeDisposed();
    }

    // Further tests are omitted

    private sealed class UpdateProductsSessionMock : AsyncTransactionalSessionMock, IUpdateProductsSession
    {
        public List<Product> Products { get; } = Generate500Products();

        public List<Product> UpdatedProducts { get; } = new ();

        public Task<int> GetProductsCountAsync() => Task.FromResult(Products.Count);

        public Task<List<Product>> GetProductBatchAsync(int skip, int take) =>
            Task.FromResult(
                Products.Skip(skip)
                        .Take(take)
                        .ToList()
            );

        public Task UpdateProductAsync(Product product)
        {
            UpdatedProducts.Add(product);
            return Task.CompletedTask;
        }

        private List<Product> Generate500Products() => /* Implementation is omitted for brevity's sake */;
    }
}

In the above unit test, the session is mocked by deriving from AsyncTransactionalSessionMock. The session is injected into the constructor of the job object using an async factory mock. Via the Transactions property, you can check which transactions were created. The base class also gives you the AllTransactionsMustBeCommitted method that checks that each captured transaction was committed exactly once.

The transactional session mocks provide you with these assertion methods:

AllTransactionsMustBeCommitted: checks if all transactions were committed.
AllTransactionsExceptTheLastMustBeCommitted: checks if all transactions are committed, except the last one which must be rolled back. Useful for scenarios where the first failing transaction should stop the whole job.
TransactionsWithIndexesMustBeCommitted: allows you to specify the transactions that should be committed. Simply pass in the indexes of the corresponding transactions. Especially useful when combined with TransactionsWithIndexesMustBeRolledBack.
AllTransactionsMustBeRolledBack: checks that no transaction was committed.
TransactionsWithIndexesMustBeRolledBack: checks that the specified transactions were rolled back. Simply pass in the indexes of the corresponding transactions. Especially useful when combined with TransactionsWithIndexesMustBeCommitted.
MustBeDisposed: checks if the specified session as well as all tracked transactions were disposed.