Dependency injection in Xunit project

Question

I am working on an ASP.Net Core MVC Web application.

My Solution contains 2 projects:

• One for the application and
• A second project, dedicated to unit tests (XUnit).

I have added a reference to the application project in the Tests project.

What I want to do now is to write a class in the XUnit Tests project which will communicate with the database through entity framework.

What I was doing in my application project was to access to my DbContext class through constructor dependency injection.

But I cannot do this in my tests project, because I have no Startup.cs file. In this file I can declare which services will be available.

So what can I do to get a reference to an instance of my DbContext in the test class?

Armentrout

Try this xunit di support built into xunit framework: nuget.org/packages/Xunit.Di, so that you can inject services dependencies the same way as you do for any other applications. – Whitleather

Answer 1

You can implement your own service provider to resolve DbContext.

public class DbFixture
{
    public DbFixture()
    {
        var serviceCollection = new ServiceCollection();
        serviceCollection
            .AddDbContext<SomeContext>(options => options.UseSqlServer("connection string"),
                ServiceLifetime.Transient);

        ServiceProvider = serviceCollection.BuildServiceProvider();
    }

    public ServiceProvider ServiceProvider { get; private set; }
}

public class UnitTest1 : IClassFixture<DbFixture>
{
    private ServiceProvider _serviceProvider;

    public UnitTest1(DbFixture fixture)
    {
        _serviceProvider = fixture.ServiceProvider;
    }

    [Fact]
    public void Test1()
    {
        using (var context = _serviceProvider.GetService<SomeContext>())
        {
        }
    }
} 

But bear in your mind using EF inside a unit test is not a good idea and it's better to mock DbContext.

The Anatomy of Good Unit Testing

Barbary

What is DatabaseSeeder ? Should i put DbFixture in a Service subfolder ? – Armentrout

Oops copy paste mistake. You can put DbFixture anywhere inside test project. I create TestSetup or TestInfrastructure folder and put such classes in these folders. – Barbary

Instead of your line with AddEntityFrameworkSqlServer, i am using this: serviceCollection.AddDbContext<BDDContext>(options => options.UseSqlServer("connection string") Is there a big difference ? – Armentrout

No both works fine and AddEntityFrameworkSqlServer registers additional services. – Barbary

One more thing: Are you sure i do not have to "declare" this DbFixture class somewhere ? I have a warning which says the class is never instancied and i have a runtime error: The following constructor parameters did not have matching fixture data: DbFixture fixture – Armentrout

hi @MohsenEsmailpour can you answer this question here, I need to grab all services, and use them on call for integration next, not just db context, Thanks ! #57331895 – Athanor

#57331895 this is another great question – Alfi

@AlanWalker Sure I will check the question ASAP. – Barbary

Tried to create a sample but didn't run (LinqPad 6: Query -> Add XUnit Test Support and then pasted your code; which is usually a good starting point for testing). How to reference ServiceCollection, ServiceLifetime, ServiceProvider? And could you give a short snippet for SomeContext? – Ireful

The Anatomy of Good Unit Testing - unfortunately the link you provided is broken, could you look it up and fix it please? – Ireful

Important: .UseSqlServer needs Microsoft.EntityFrameworkCore.SqlServerpackage to be loaded. This is due to reported issue #7891 wit EF Core. – Ireful

Ok, to test this I used Adventureworks, added class SomeContext with public SomeContext(DbContextOptions options) : base(options) and public DbSet<AWBuildVersion> AWBuildVersions { get; set; }, implemented AWBuildVersion with all properties and added query context.AWBuildVersions.Select(s=>s.DatabaseVersion).FirstOrDefault().Dump(); to the using statement in the code snippet. This query gives me the error The entity type 'AWBuildVersion' requires a primary key to be defined.` - but I used the [Key] attribute for SystemInformationID. Do you have any idea how to get it working? – Ireful

After using [Key], [Table("TableName")] and [Column("ColumName"] annotations it was still not working. Then I found why: I had defined the properties in the table class "as is", i.e. without { get; set; } - after adding that it was working fine! – Ireful

@Ireful I fixed the broken link. – Barbary

@MohsenEsmailpour - Thank you, that is indeed a nice summary how to properly design (write) unit tests. – Ireful

Answer 2

You can use Xunit.DependencyInjection

Micrometeorology

Expanding on what this does and why it's better than other approaches would be super useful here. Also adding a small sample demonstrating how it looks when used would be great . – Pickle

#63269960 Working through the problem – Concent

Answer 3

For unit tests you need to mock your context.

There is a great nuget package for mocking that is called Moq.

Some help to get you started:

public ClassName : IDisposable
{
    private SomeClassRepository _repository;
    private Mock<DbSet<SomeClass>> _mockSomeClass;

    public ClassName() 
    {
        _mockSomeClass = new Mock<DbSet<SomeClass>>();

        var mockContext = new Mock<IApplicationDbContext>();
        mockContext.SetupGet(c => c.SomeClass).Returns(_mockSomeClass.Object);

        _repository = new SomeClassRepository(mockContext.Object);
    }

    public void Dispose()
    {
        // Anything you need to dispose
    }

    [Fact]
    public void SomeClassTest()
    {
        var someClass = new SomeClass() { // Initilize object };

        _mockSomeClass.SetSource(new[] { someClass });

        var result = _repository.GetSomethingFromRepo( ... );

        // Assert the result
    }
}

For integration tests you do the same thing but the setup is:

_context = new ApplicationDbContext();

Make sure that your TestClass inherits from IDisposable (TestClass : IDisposable) so that you can dispose the context after each test.

https://xunit.github.io/docs/shared-context

Whirlybird

There's no SetUp, atrribute in xunit. Use constructor instead. – Sump

Answer 4

You can to use package Microsoft.EntityFrameworkCore.InMemory

var _dbContextOptions = new DbContextOptionsBuilder<DbContext>().UseInMemoryDatabase(Guid.NewGuid().ToString()).Options;

And then

var context = new DbContext(_dbContextOptions);

Brick