Durable Azure Functions and Integration Tests

I'm trying to test (integration tests) my Azure Durable Function v3 with SpecFlow and MSTest.

Functions are initialized with DI and Startup class:

[assembly: FunctionsStartup(typeof(Startup))]
namespace MyNamespace.Functions
{
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            ConfigureServices(builder.Services);
        }
...

Orchestrator entry point is triggered by HTTP endpoint:

public class Function1
{
    [FunctionName(nameof(Function1))]
    public async Task<IActionResult> DoYourJob(
        [HttpTrigger(AuthorizationLevel.Anonymous, methods: "post", Route = "api/routes/function1")] HttpRequestMessage httpRequest,
        [DurableClient] IDurableOrchestrationClient starter)
        {
...

My IntegrationTest constructor initializes Az Function with HostBuilder (thanks to this article):

[Binding]
public sealed class Function1StepDefinitions
{
    private readonly IHost _host;
    private readonly Function1 _function;

    public Function1StepDefinitions()
    {
        var startup = new MyNamespace.Functions.Startup();
        _host = new HostBuilder()
            .ConfigureWebJobs(config =>
            {
                config.AddDurableTask(options =>
                {
                    options.HubName = "MyTaskHub";
                });

                startup.Configure(config);
            })
            .ConfigureServices(ReplaceTestOverrides)  // Method to replace/mock some external services
            .Build();

        _function = new Function1(Host.Services.GetRequiredService<IOptions..., ..);

And in my test I dont know how to retrieve IDurableOrchestrationClient to call my HTTP Trigger:

    [When(@"I call my function")]
    public async Task WhenICallMyFunction()
    {
        var request = new HttpRequestMessage();

        await _function.DoYourJob(
            request,
            Host.Services.GetService<IDurableOrchestrationClient>()); // This is always null
...

Is there a way to retrieve this IDurableOrchestrationClient and test my whole Function (with Orchestrator and Activities calls)?