C#•2mo ago

Unit Testing ASP.NET async api service

Okay. I am trying to make a unit test for my Customer Service. I tried starting with the Read operation which looks like this in my service:

public async Task<Customer> Read(int customerId)
{
    return await _context.Customers
        .FirstOrDefaultAsync(c => c.CustomerId == customerId);
}

public async Task<Customer> Read(int customerId)
{
    return await _context.Customers
        .FirstOrDefaultAsync(c => c.CustomerId == customerId);
}

I tried using this as a guide: https://learn.microsoft.com/en-us/ef/ef6/fundamentals/testing/mocking#testing-query-scenarios

Testing with a mocking framework - EF6

Testing with a mocking framework in Entity Framework 6

17 Replies

mellowzippyOP•2mo ago

I tried implementing it myself like this:

[Theory]
[InlineData(0)]
[InlineData(1)]
[InlineData(5)]
[InlineData(6)]
public async Task CustomerRead(int customerId)
{
    // Arrange
    var data = new List<Customer>
    {
        new() { CustomerId = 1, Email = "[email protected]", FirstName = "Willy", LastName = "the Nilly" },
        new() { CustomerId = 2, Email = "[email protected]", FirstName = "Billy", LastName = "the Hilly" },
        new() { CustomerId = 3, Email = "[email protected]", FirstName = "Silly", LastName = "the Trippy" },
        new() { CustomerId = 4, Email = "[email protected]", FirstName = "Jeffrey", LastName = "Geoff" },
        new() { CustomerId = 5, Email = "[email protected]", FirstName = "John", LastName = "Smith" }
    }.AsQueryable();

    var mockSet = new Mock<DbSet<Customer>>();

    mockSet.As<IQueryable<Customer>>().Setup(m => m.Provider).Returns(data.Provider);
    mockSet.As<IQueryable<Customer>>().Setup(m => m.Expression).Returns(data.Expression);
    mockSet.As<IQueryable<Customer>>().Setup(m => m.ElementType).Returns(data.ElementType);
    mockSet.As<IQueryable<Customer>>().Setup(m => m.GetEnumerator()).Returns(data.GetEnumerator());

    var mockContext = new Mock<TheatreDbContext>(new DbContextOptions<TheatreDbContext>());
    mockContext.Setup(c => c.Customers).Returns(mockSet.Object);

    var service = new CustomerService(mockContext.Object);

    // Act
    var foundCustomer = await service.Read(customerId);

    // Assert
    if (customerId == 0 || customerId == 6)
    {
        Assert.Null(foundCustomer);
    }
    else
    {
        Assert.NotNull(foundCustomer);
        Assert.IsType<Customer>(foundCustomer);
        Assert.Equal(customerId, foundCustomer.CustomerId);
    }
}

[Theory]
[InlineData(0)]
[InlineData(1)]
[InlineData(5)]
[InlineData(6)]
public async Task CustomerRead(int customerId)
{
    // Arrange
    var data = new List<Customer>
    {
        new() { CustomerId = 1, Email = "[email protected]", FirstName = "Willy", LastName = "the Nilly" },
        new() { CustomerId = 2, Email = "[email protected]", FirstName = "Billy", LastName = "the Hilly" },
        new() { CustomerId = 3, Email = "[email protected]", FirstName = "Silly", LastName = "the Trippy" },
        new() { CustomerId = 4, Email = "[email protected]", FirstName = "Jeffrey", LastName = "Geoff" },
        new() { CustomerId = 5, Email = "[email protected]", FirstName = "John", LastName = "Smith" }
    }.AsQueryable();

    var mockSet = new Mock<DbSet<Customer>>();

    mockSet.As<IQueryable<Customer>>().Setup(m => m.Provider).Returns(data.Provider);
    mockSet.As<IQueryable<Customer>>().Setup(m => m.Expression).Returns(data.Expression);
    mockSet.As<IQueryable<Customer>>().Setup(m => m.ElementType).Returns(data.ElementType);
    mockSet.As<IQueryable<Customer>>().Setup(m => m.GetEnumerator()).Returns(data.GetEnumerator());

    var mockContext = new Mock<TheatreDbContext>(new DbContextOptions<TheatreDbContext>());
    mockContext.Setup(c => c.Customers).Returns(mockSet.Object);

    var service = new CustomerService(mockContext.Object);

    // Act
    var foundCustomer = await service.Read(customerId);

    // Assert
    if (customerId == 0 || customerId == 6)
    {
        Assert.Null(foundCustomer);
    }
    else
    {
        Assert.NotNull(foundCustomer);
        Assert.IsType<Customer>(foundCustomer);
        Assert.Equal(customerId, foundCustomer.CustomerId);
    }
}

But when I run dotnet test it tells me:

The provider for the source 'IQueryable' doesn't implement 'IAsyncQueryProvider'. Only providers that implement 'IAsyncQueryProvider' can be used for Entity Framework asynchronous operations.

. And because this is me writing my first test I have absolutely no clue what this means. And I don't really know where to start to debug it. I tried adding the "TestDbAsyncQueryProvider" code they provided but it changed absolutely nothing in the error so it didn't help me to fix it. $paste

MODiX•2mo ago

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mellowzippyOP•2mo ago

Full error: https://paste.mod.gg/byjidngksegg/0

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mellowzippyOP•2mo ago

I was able to test it if I made my service (and the test) synchronous, the error only came when I tried to make it async.

mellowzippyOP•2mo ago

https://tenor.com/view/elmo-stare-sesame-street-rocco-death-stare-gif-24438342

Tenor

mellowzippyOP•2mo ago

If one looks at this code and thinks that it is quite the mess, I would appreciate perhaps good videos or websites on how to do this correctly.

Sossenbinder•2mo ago

I'm on my phone and can't comment on your mocking setup, but as a general guidance I'd probably not test ef core logic since it's not something maintained by yourself. If you have complex enough queries to warrant a test, I'd always favor an integration test with test containers of the database you'll actually run with in the end Since you get to test the sql translation which will actually take place later on If you mock things or use an in memory ef core db, then you're kinda ripping out 80% of the code and your test has little representation of what's going on

mellowzippyOP•2mo ago

What are integration tests used for? Because (for now) it is only an API. Not connected to any other program so it's not "integrated" with anything right?

Sossenbinder•2mo ago

If you use ef, you'd probably be integrating with a database It qualifies as another system you integrate with

mellowzippyOP•2mo ago

Ooo okay Would you happen to have any links that show how to do proper integration testing?

Sossenbinder•2mo ago

There's a good msdn article for integration tests with asp net core https://learn.microsoft.com/en-us/aspnet/core/test/integration-tests?view=aspnetcore-8.0. This might get you the general idea 👍 If you ask me, I'd definitely recommend reading on testcontainers as well if you're doing integration testing in any form, but I feel like you're just getting started with testing, so taking it step by step is a good idea 👍

Integration tests in ASP.NET Core

Learn how integration tests ensure that an app's components function correctly at the infrastructure level, including the database, file system, and network.

mellowzippyOP•2mo ago

Thank you @Sossenbinder Do you think I should drop the unit tests than? then* Or perhaps use them to test something differently?

Sossenbinder•2mo ago

This wouldn't be something I'd unit test, no. I mainly unit test complex logic and try to keep the dependencies to external systems pretty clean within, so I don't have to rely on mocking and can just pass input and output. When it comes to database interaction which warrants testing, I usually reach out for integration tests

mellowzippyOP•2mo ago

Is there anything I should unit test in my API? Don't know what would be complex logic. I feel like my API is pretty simple just CRUD mostly

Sossenbinder•2mo ago

That depends on your code I assume. If it's a pretty basic crud api without much logic, it might not be something which contains a lot of unit testable code

Sossenbinder•2mo ago

https://enterprisecraftsmanship.com/posts/when-to-mock/ Here's another great link. Generally recommend vladimir khorikov for testing theory, his book is great

Enterprise Craftsmanship

When to Mock

The use of mocks in unit testing is a controversial topic (maybe less so now than several years ago). I remember how, throughout my programming career, I went from mocking almost every dependency, to the "no-mocks" policy, and then to "only mock external dependencies". None of this practices are good enough. In this article, I’ll show you whi...

mellowzippyOP•2mo ago

Okayyy I will try to use this, thanks a lot

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Unit Testing ASP.NET async api service