How to test a Ninject Factory returns the same instance in RequestScope

Question

In a WebApi application, I am using Ninject to inject a factory that allows consuming classes to create a DbContext that is scoped according to their requirements. I want to be able to write a unit test that verifies that two calls to the same factory for a Request scoped context return the same instance.

The factory interface is:

public interface IContextFactory
{
    IMyContext GetContext();
    IMyContext GetTransientContext();
}

The Ninject configuration looks like this:

 Bind<IContextFactory>().ToFactory();
 Bind<IMyContext>().To<MyContext>()
     .InRequestScope()
     .NamedLikeFactoryMethod((IContextFactory f) => f.GetContext());
 Bind<IMyContext>().To<MyContext>()
     .InTransientScope()
     .NamedLikeFactoryMethod((IContextFactory f) => f.GetTransientContext());

My unit test is as follows:

[Fact]
public void RequestScopedContextAlwaysSame()
{
    // Arrange
    NinjectWebCommon.Start();
    var factory = (IContextFactory)NinjectWebCommon.Bootstrapper.Kernel.GetService(typeof(IContextFactory));

    //Act
    var context1 = factory.GetContext();
    var context2 = factory.GetContext();

    //Assert
    Assert.Same(context1, context2);
}

I expected the both calls to the factory to return the same instance, but in fact they are two different instances. I think this is a testing error as in the application, I have been able to successfully verify that the same instance is injected into different consumers when they call the GetContext() method.

I suspect this is not working in a unit test because there is no HttpContext and InRequestScope() depends on it. Is there a way round this?

jbl · Accepted Answer · 2019-08-13T09:33:20.173

I suspect this is not working in a unit test because there is no HttpContext and InRequestScope() depends on it.

I think you are right. You may try :

 Bind<IMyContext>().To<MyContext>()
     .InScope(ctx => this.Scope)
     .NamedLikeFactoryMethod((IContextFactory f) => f.GetContext());

where this.Scope is a property of your Test class (any reference type will be ok) the value of which is initialized upon your test setup

Alternatively, if you still want to use the InRequestScope syntax, you may try :

    public class MyPlugin : INinjectHttpApplicationPlugin
    {
        private Object Scope { get; } = true;

        public void Dispose(){}

        public INinjectSettings Settings { get; set; }

        public object GetRequestScope(IContext context)
        {
            return Scope;
        }

        public void Start() { }

        public void Stop() { }
    }

Then your test would be something like :

    public void RequestScopedContextAlwaysSame()
    {
        var kernel = new StandardKernel();
        kernel.Components.Add<INinjectHttpApplicationPlugin, MyPlugin>();
        kernel.Bind<IContextFactory>().ToFactory();
        kernel.Bind<IMyContext>().To<MyContext>()
            .InRequestScope()
            .NamedLikeFactoryMethod((IContextFactory f) => f.GetContext());
        kernel.Bind<IMyContext>().To<MyContext>()
            .InTransientScope()
            .NamedLikeFactoryMethod((IContextFactory f) => f.GetTransientContext());

        var factory = kernel.Get<IContextFactory>();
        //Act
        var context1 = factory.GetContext();
        var context2 = factory.GetContext();

        //Assert
        Assert.IsTrue(context1.Equals(context2));
    }

It's a good idea, but I then wouldn't really be testing the Ninject configuration creates the desired result. — Paul Taylor, Aug 12 '19 at 17:53

How to test a Ninject Factory returns the same instance in RequestScope

1 Answers1