NSubstitute | A friendly substitute for .NET mocking libraries | Unit Testing library

It seems that the issue you're having is not related to AutoFixture but rather with NSubstitute.

Since ITransaction is an interface AutoFixture will delegate the task of creating and instance to the mocking library. In your case that's NSubstitute.

Since your interface only declares getters but no setters, NSubstitute will generate a dynamic proxy, for your interface, that as will as well not have any public setters. This is why AutoFixture is unable to set the values of your properties.

So if you want to continue using the mock, you'll have to either specify a public setter in your interface or tell AutoFixture how to set the values using the NSubstitute API. Unfortunately you'll be able to implement the second option only by implementing an ISpecimenBuilder factory for your interface and then play with reflection.

Another way, which is what I recommend, is to relay the setup of your interface to a fake implementation, which you'll create by hand and which will have the public setters. Then you'll instruct AutoFixture to relay all requests to the interface to your fake class.

Answering my own question...

The issue was that I didn't have a test case where customer.Dead.HasValue == false, or said another way, where customer.Dead == null. The database and entity allow for a null value here, but there was no unit test of null.

I have the following code in my class under testing:

devices = ContainerLocator.Container.Resolve();

That's the reason why you don't inject the container. In fact, you avoid using the container at all except during the registration phase and the initial call to Resolve.

So my question is how could I make a substitution for ContainerLocator.Container?

The answer's: you don't

What you should do instead is to let the container do the resolving work by injecting what you actually want, not the almighty container.

Because DepClass is neither an interface nor an abstract type, by default, AutoFixture will not rely on a mocking framework to create the instance, and will use the actual constructor from the type.

Since NSubstitute does not have the equivalent of Mock or Fake from other popular mocking frameworks, AutoFixture had to provide a special specimen builder, called SubstituteRelay, to fill in the gap. You can use this class as any other specimen builder to instruct the Fixture to return a mock when a specific type instance is requested.

You need to include the IncludeTestAssembly property to work:

You can mock LoadData to return a task managed by you, which will complete when you say so. Then, do not await Refresh because for this test you don't need for Refresh to complete, you want to check the state in progress. Then after you call Refresh (without await) the LoadData will be in progress and you can verify that state is Busy. Then complete the LoadData and wait for Refresh to complete to finish the test. For example:

Thanks for the repo. I believe this is occurring as the process of stubbing the second call ends up invoking the first stub with a null argument (Arg.Is returns null). NSubstitute realises that this call doesn't match, and so handles the NullReferenceException. The test should still work as required -- it just affects debugging when "break on exception" is enabled.

If you update to NSubstitute 4.x this case should be handled without the exception as there is some code to detect that a call is being stubbed and so the first stub will not be checked.

You cannot mock a local variable. You can create a virtual method which will return QuickbooksBO and substitute it.

AutoFixture can only build upon the testing framework only as much as it allows itself to be extended. In xUnit 2 each provided DataAttribute is considered, a distinct provider of arguments for the test, which is why they are isolated during runtime.

The recommended option here is to create a data attribute that will apply both AutoMoq and the AutoMapper customization.

You can achieve this by using a CompositeCustomization and then using it in a custom AutoDataAttribute implementation.