How to get an instance of IServiceProvider in .NET Core?

As goaty mentioned it’s enough to create new ServiceCollection. Here’s example class which can be used to access DI container in .NET Core:

public static class ServiceProviderFactory
{
    public static IServiceProvider ServiceProvider { get; }

    static ServiceProviderFactory()
    {
        HostingEnvironment env = new HostingEnvironment();
        env.ContentRootPath = Directory.GetCurrentDirectory();
        env.EnvironmentName = "Development";

        Startup startup = new Startup(env);
        ServiceCollection sc = new ServiceCollection();
        startup.ConfigureServices(sc);
        ServiceProvider = sc.BuildServiceProvider();
    }
}

Startup class is taken from tested project so the service registrations don’t need to be repeated.

Then in test class simply use:

var foo = ServiceProviderFactory.ServiceProvider.GetServices(typeof(IFoo));