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c#unit-testingautofixture
Tim Pickin
Tim Pickin

Reputation: 419

Autofixture Constructer injection lazy loading

I am using autofixture in my unit tests and it is great the way that it works as an automocker.

However I have a problem when injecting a lazy loaded object into my class. For example:

public class MyClass : IMyClass
{
    private Lazy<IMyInjectedClass> _myInjectedClassLazy;
    private IMyInjectedClass _myInjectedClass {
        get { return _myInjectedClassLazy.Value; }
    }

    public MyClass(Lazy<IMyInjectedClass> injectedClass)
    {
        _myInjectedClassLazy = _myInjectedClass;
    }

    public void DoSomething()
    {
        _myInjectedClass.DoSomething();
    }
}

Then when I try to run a test where I use autofixture to generate the class as so:

public class MyTests
{
    [Test]
    public void ShouldDoSomething()
    {
        var fixture = new Fixture().Customize(new AutoMoqCustomization());
        fixture.Behaviors.Remove(new ThrowingRecursionBehavior());
        fixture.Behaviors.Add(new OmitOnRecursionBehavior());

        var mockMyClass = fixture.Freeze<Mock<IMyClass>>();

        var sut = fixture.Create<MyClass>();

        sut.DoSomething();
    }
}

But this code throws the following error:

System.MissingMemberException : The lazily-initialized type does not have a public, parameterless constructor.

Is there a way that I can avoid this error and inject lazy objects when using autofixture?

Upvotes: 2

Views: 1253

Answers (1)

Mark Seemann
Mark Seemann

Reputation: 233377

FWIW, although I disagree with the motivation for doing this, you can tell AutoFixture how to create an instance of Lazy<IMyInjectedClass>:

var fixture = new Fixture().Customize(new AutoMoqCustomization());
fixture.Behaviors.Remove(new ThrowingRecursionBehavior());
fixture.Behaviors.Add(new OmitOnRecursionBehavior());
fixture.Register(                                                   // Add this 
    (IMyInjectedClass x) => new Lazy<IMyInjectedClass>(() => x));   // to pass

var mockMyClass = fixture.Freeze<Mock<IMyClass>>();

var sut = fixture.Create<MyClass>();

sut.DoSomething();

If you need to do this repeatedly, you should consider packaging this in a Customization.

Upvotes: 1

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