How to use DependencyInjection in TestKit

[shawndewet]

I have an actor that initializes a child actor like so:

public AccountActor(string accountId)
        {
            PersistenceId = $"Account-" + accountId;
            State = new AccountState();
            var dbWriterActorProps = Akka.DependencyInjection.DependencyResolver.For(Context.System).Props<AccountDbWriter>();
            _dbWriterActor = Context.ActorOf(dbWriterActorProps, $"DbWriterActor-{PersistenceId}");

The DependencyResolver resolves dependencies for the AccountDbWriter child actor (specifically, IServiceProvider (which is used inside DbWriterActor to create a scope and resolve a DbContext).

The above works fine when I run the system. But I'm trying to write tests for this AccountActor, and what I can't figure out is how to override the DependencyResolver in my TestKit-based test fixture, so as to have it resolve mock instances that I want to provide with Moq.

Please advise on how this can be done?

More context:
In my test fixture, I have this setup to mock IServiceProvider so that it returns an an InMemorySqlDatabase.

var optionsBuilder = new DbContextOptionsBuilder<CypherDbContext>();
            optionsBuilder.UseInMemoryDatabase("AccountActorTests");

            var serviceProvider = new Mock<IServiceProvider>();
            serviceProvider
                .Setup(x => x.GetService(typeof(CypherDbContext)))
                .Returns(new CypherDbContext(optionsBuilder.Options));

            var serviceScope = new Mock<IServiceScope>();
            serviceScope.Setup(x => x.ServiceProvider).Returns(serviceProvider.Object);

            var serviceScopeFactory = new Mock<IServiceScopeFactory>();
            serviceScopeFactory
                .Setup(x => x.CreateScope())
                .Returns(serviceScope.Object);

            serviceProvider
                .Setup(x => x.GetService(typeof(IServiceScopeFactory)))
                .Returns(serviceScopeFactory.Object);

More context, the DbWriterActor that the AccountActor (sut) creates as its child, is defined as follows:

public AccountDbWriter(IServiceProvider serviceProvider)
        {
            _serviceProvider = serviceProvider;
            ReceiveAsync<SaveProjection>(async message =>
            {
                using IServiceScope serviceScope = _serviceProvider.CreateScope();
                var cypherDbContext = serviceScope.ServiceProvider.GetService<CypherDbContext>();

What I can't figure out is how to get TestKit's .Sys to use the above mocked IServiceProvider in its DependencyInjection setup, such that when AccountActor creates its child DbWriterActor, the mocked IServiceProvider get DI'd into the child.

Please help.

[shawndewet]

Ok I figured it out!!

You need a method that will set up a mock IServiceProvider. Here's mine using Moq:

private static IServiceProvider SetupMockServiceProvider()
        {
            var optionsBuilder = new DbContextOptionsBuilder<CypherDbContext>();
            optionsBuilder.UseInMemoryDatabase("ActorTests");

           //mock the DbContext call
            var mockServiceProvider = new Mock<IServiceProvider>();
            mockServiceProvider
                .Setup(x => x.GetService(typeof(CypherDbContext)))
                .Returns(new CypherDbContext(optionsBuilder.Options));

            mockServiceProvider
                .Setup(x => x.GetService(typeof(IServiceProvider)))
                .Returns(mockServiceProvider.Object); //this part is key...a request for GetService<IServiceProvider> should return the mocked Service Provider itself.

            var serviceScope = new Mock<IServiceScope>();
            serviceScope.Setup(x => x.ServiceProvider).Returns(mockServiceProvider.Object);

            var serviceScopeFactory = new Mock<IServiceScopeFactory>();
            serviceScopeFactory
                .Setup(x => x.CreateScope())
                .Returns(serviceScope.Object);

            mockServiceProvider
                .Setup(x => x.GetService(typeof(IServiceScopeFactory)))
                .Returns(serviceScopeFactory.Object);

            return mockServiceProvider.Object;
        }

Then in the constructor of the TestFixture, you pass this mocked IServiceProvider to the TestKit base constructor like so:

public class AccountActorTests : TestKit {
    public AccountActorTests()
            : base(ActorSystemSetup.Create()
                 .And(DependencyResolverSetup.Create(SetupMockServiceProvider())))