xUnit - Using WebApplicationFactory with CollectionFixture for .Net Core Integration Tests

Question

I have implemented Integration Tests for my .Net Core API using xUnit, shared Class Fixtures, and dependency injection so I can use WebApplicationFactory.

public class DatabaseFixture : WebApplicationFactory<Startup> {
    public DatabaseFixture(WebApplicationFactory<Startup>) {
        //Initialize Stuff
    }
}

public class SaveTests : IClassFixture<DatabaseFixture> {
    private DatabaseFixture databaseFixture;

    public SaveTests(DatabaseFixture databaseFixture)
    {
        this.applicationFixture = applicationFixture;
    }

    //Tests.....
}

public class SaveTests2 : IClassFixture<DatabaseFixture> {
    private DatabaseFixture databaseFixture;

    public SaveTests2(DatabaseFixture databaseFixture)
    {
        this.applicationFixture = applicationFixture;
    }

    //Tests.....
}

This has worked well, but, the Test Data is initialized for each test file.

I am looking to update my tests to use a Collection Fixture instead of a Class Fixture however I have been unable to implement a Collection Fixture while injecting WebApplicationFactory.

[CollectionDefinition("SaveTestCollection")]
public class SaveTestCollectionFixture : ICollectionFixture<DatabaseFixture>
{
}

public class DatabaseFixture : WebApplicationFactory<Startup> {
    public DatabaseFixture(WebApplicationFactory<Startup>) {
        //Initialize Stuff
    }
}

[Collection("SaveTestCollection")]
public class SaveTests
{
    DatabaseFixture fixture;

    public SaveTests(DatabaseFixture fixture)
    {
        this.fixture = fixture;
    }
}

The error I get is:

System.AggregateException : One or more errors occurred. (Collection fixture type 'DatabaseFixture' had one or more unresolved constructor arguments: WebApplicationFactory) (The following constructor parameters did not have matching fixture data: DatabaseFixture fixture)
---- Collection fixture type 'DatabaseFixture' had one or more unresolved constructor arguments: WebApplicationFactory`1 factory
---- The following constructor parameters did not have matching fixture data: DatabaseFixture fixture

I understand that the Dependency Injection is failing, but I am not sure how to fix it.

So my question is, am I able to include the WebApplicationFactory via Dependency Injection, or do I need to change how I am using WebApplicationFactory to work with Collection Fixtures?

Any help is greatly appreciated

Answer 1

Ended up implementing the following solution, which is documented on the XUnit Github page:

• Continue using IClassFixture
• Only fully execute the fixture constructor the first time in, and keep a static reference to the fully initialized fixture
• Any additional instances of the fixture constructor exit early, and do not re-generate the test data
• All Test files reference the static fixture instead of the fixture passed into the test constructor
• The fixture still needs to be passed into the test constructor so the fixture constructor is fully executed when it is needed

Main Collection to provide the WebApplicationFactory

[CollectionDefinition("Tests")]
public class FixtureCollection : ICollectionFixture<WebApplicationFactory<Startup>>
{

}

• Fixture uses the Injected WebApplicationFactory to initalize the test data.
• There is now a static property that keeps a reference to an instance of the fixture
• If the static Instance has not been defined, run fixture initialization, and set the static instance to reference this instance of the fixture
• If the static Instance has been defined, do not run fixture initialization
• This ensures that the Database data is only generated once, no matter how many times the fixture is used

public class SaveTestDatabaseFixture : WebApplicationFactory<Startup>{

    public static SaveTestDatabaseFixture Instance;

    public TestData first_test_data { get; set; }

    public SaveTestDatabaseFixture(WebApplicationFactory<Startup> factory)
    {
          if (Instance != null)
          {
              return;
          }

          var context = factory.GetContext();
          ......
          first_test_data = new TestData();
          context.TestData.Add(first_test_data);
          context.SaveChanges();

          Instance = this;
    }
}

All tests use the static instance of the Database Fixture.

[Collection("Tests")]
public class TestDataTests : IClassFixture<SaveTestDatabaseFixture> {
    private readonly SaveTestDatabaseFixture databaseFixture;

    public TestDataTests (SaveTestDatabaseFixture _)
    {
        this.databaseFixture = SaveTestDatabaseFixture.Instance;
    }

    [Fact]
    public async Task Test1()
    {
        var x = databaseFixture.TestData.Id;
        //Run Test
    }
}

[Collection("Tests")]
public class TestData2Tests : IClassFixture<SaveTestDatabaseFixture> {
    private readonly SaveTestDatabaseFixture databaseFixture;

    public TestData2Tests (SaveTestDatabaseFixture _)
    {
        this.databaseFixture = SaveTestDatabaseFixture.Instance;
    }

    [Fact]
    public async Task Test2()
    {
        var x = databaseFixture.TestData2.Id;
        //Run Test
    }
}

As I have quite a few separate test files, this change reduced the amount of data being saved to the Test Database by 90% (2000 rows down to 200 rows). It also reduced the execution time of the test suite (including Database setup time) from from 53 seconds to 20 seconds.