Category: Testing

Lets start with simple controller:

[Route("api/[controller]")
public class TestController : Controller
{
	[HttpGet("")]
	public IActionResult Get()
	{
		return Ok();
	}
}

Now we want to create unit test for this method using AutoFixture/Moq/Shouldly/XUnit stack:

public class TestControllerTests 
{
	[Theory, AutoMoqData]
	public void Get_ShouldReturn_HttpStatusOk(TestController sut)
	{
		// act..
		var actual = sut.Get();

		// assert..
		actual.ShouldNotBeNull();
		actual.ShouldBeOfType()
	}
}

Test runner will crash saying:

AutoFixture.ObjectCreationException : AutoFixture was unable to create an instance from Microsoft.AspNetCore.Mvc.ViewFeatures.ViewDataDictionary because creation unexpectedly failed with exception. Please refer to the inner exception to investigate the root cause of the failure.

Request path:
	  J2BI.Holidays.TravelDocs.Api.Controllers.AccommodationController sut --> 
	   J2BI.Holidays.TravelDocs.Api.Controllers.AccommodationController --> 
	    Microsoft.AspNetCore.Mvc.ViewFeatures.ViewDataDictionary ViewData --> 
	     Microsoft.AspNetCore.Mvc.ViewFeatures.ViewDataDictionary


---- System.Reflection.TargetInvocationException : Exception has been thrown by the target of an invocation.
-------- Castle.DynamicProxy.InvalidProxyConstructorArgumentsException : Can not instantiate proxy of class: Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata.
Could not find a parameterless constructor.

The problem lies in lack of parameterless constructor for ModelMetadata class.
This can easily be fixed with AutoFixture customization:

public class ApiControllerCustomization : ICustomization
{
    public void Customize(IFixture fixture)
    {
        fixture.Register(() => new CustomCompositeMetadataDetailsProvider());
        fixture.Inject(new ViewDataDictionary(fixture.Create(), fixture.Create()));
    }

    private class CustomCompositeMetadataDetailsProvider : ICompositeMetadataDetailsProvider
    {
        public void CreateBindingMetadata(BindingMetadataProviderContext context)
        {
            throw new System.NotImplementedException();
        }

        public void CreateDisplayMetadata(DisplayMetadataProviderContext context)
        {
            throw new System.NotImplementedException();
        }

        public void CreateValidationMetadata(ValidationMetadataProviderContext context)
        {
            throw new System.NotImplementedException();
        }
    }
}

This now has to be wrapped in data attribute:

public class AutoApiMoqDataAttribute : AutoDataAttribute
{
    public AutoApiMoqDataAttribute()
        : base(() =>
        {
            var fixture = new Fixture();

            fixture.Customize(new ApiControllerCustomization())
                   .Customize(new AutoMoqCustomization())
                   .Behaviors.Add(new OmitOnRecursionBehavior());

            return fixture;
        })
    {
    }
}

Voila! Now the test will pass.

Check out this gist