Deeper integration with mocking frameworks

[egil]

To enable automatic mocking of services required by components, e.g. when using AutoFixture in combination with a mocking framework, there should be a way to either replace the TestServicesProvider or to have it redirect to a user provided IServiceProvider when it cannot resolve a service itself.

This is inspired by the post on using AutoFixture and Moq to simplify the "arrange" step of a test, described here: #307.

[thopdev]

Hi @egil, i was looking into it. And i would like to discuss my suggestion before cleaning up etc..
My suggestion/plan:
The TestServiceProvider is available though the TestContext.
For getting services the TestServiceProvider has a function:

public object GetService(Type serviceType)
{
	if (_serviceProvider is null)
		_serviceProvider = _serviceCollection.BuildServiceProvider();

	return _serviceProvider.GetService(serviceType);
}

My plan is to alter this function with a Func like this:

public Func<Type, object> CustomerServiceCreationFunc { get; set; }

/// <inheritdoc/>
public object GetService(Type serviceType)
{

var result = CustomerServiceCreationFunc.Invoke(serviceType);

if (result != null)
return result;

if (_serviceProvider is null)
_serviceProvider = _serviceCollection.BuildServiceProvider();

return _serviceProvider.GetService(serviceType);
}

Was wondering what your opinion on it is?

[egil]

Thanks @thopdev. I'm not at home right now, but will respond in detail later.

[egil]

We are not too far apart in our thinking of this @thopdev, however, I have a slight change to the order of how things happens.

To TestServiceProvider, I want to add the following (naming tentative):

AddFallbackServiceProvider(IServiceProvider fallbackServiceProvider);

Then, the GetServices should look like this:

public object GetService(Type serviceType)
{
	if (_serviceProvider is null)
		_serviceProvider = _serviceCollection.BuildServiceProvider();

	var result = _serviceProvider.GetService(serviceType);

	if (result is null && fallbackServiceProvider is not null)
		result = fallbackServiceProvider.BuildServiceProvider();

	return result;
}

So why not call the fallback first? The idea is that 3rd party component library venders can have an e.g. ctx.SetupTelerik() method, which might add services, components to the render tree (through the RenderTree property), or configure JSInterop.

If the fallback is called first, then any services already registered that might not need to be mocked, will be, if the fallback is something like Moq or NSubstitute.

What do you think?

[thopdev]

Now i think about about the order, your right. The user should always be allowed to override the fallback.
And instead of the Func using a other IServiceProvider sounds good.

When i get time i'll start working on a PR. Not sure if i can do it today as i'm streaming tonight. But maybe i get some time before otherwise tomorrow :)

[egil]

Sounds good (where do you stream?).

This is probably a PR that will require more work with writing documentation than actual code, e.g. an extra section at the bottom of this page: https://bunit.egilhansen.com/docs/providing-input/inject-services-into-components.html

A paragraph or two that explains how the fallback logic works, and an example that shows how to utilize it with a mocking framework would be great. In other words, as short as possible, but long enough that folks get the point of the feature.

[thopdev]

Good you say that, i'll also add some documentation.
I stream at twitch (twitch.tv/thopdev) from 7pm CET. I'm creating a Blazor todo app with azure func etc.

[thopdev]

		/// <inheritdoc/>
		public object GetService(Type serviceType)
		{
			if (_serviceProvider is null)
				_serviceProvider = _serviceCollection.BuildServiceProvider();

			var result = _serviceProvider.GetService(serviceType);
			
			if (result is null && _fallbackServiceProvider is not null)
				result = _fallbackServiceProvider.GetService(serviceType);

#pragma warning disable CS8603 // Possible null reference return.
			return result;
#pragma warning restore CS8603 // Possible null reference return.
		} 
		

[thopdev]

result can still be null, i can't make the return type object? so i was wondering if you would know a better solution? @egil