Share same scoped instance between server and integration test

[jfbueno]

I've created a repo for those who want to test https://github.com/jfbueno/aspnet-testing-sameinstance

I'm trying to use the same service instance in the integration test code and the server code, but it happens that the service is constructed twice.

I created this test code to illustrate what is happening. In the constructor is created the TestServer using the same Startup as the server (which is right bellow).

The test method is getting a INumberGenerator instance using the GetService method and I am expecting that this instance that I got would be the same that the instance used in the controller, but it isn't.

Is there any way to share the same scoped instance between server and test code?

public class TestingSameServiceInstance
{
    private readonly TestServer _testServer;

    public TestingSameServiceInstance()
    {
        var hostBuilder = new WebHostBuilder()
            .UseContentRoot(Path.GetDirectoryName(Assembly.GetAssembly(typeof(Api.Startup)).Location))
            .ConfigureAppConfiguration(cb =>
            {
                cb.AddJsonFile("appsettings.json", optional: true)
                    .AddJsonFile($"appsettings.Development.json", optional: true)
                    .AddEnvironmentVariables();
            })
            .UseEnvironment("Development")
            .CaptureStartupErrors(true)
            .UseStartup<Api.Startup>();

        _testServer = new TestServer(hostBuilder);
    }

    [Fact]
    public async Task Api_Response_Should_Be_Equal_To_Value_Provided_By_Service()
    {
        using var httpClient = _testServer.CreateClient();
        var expectedNumber = _testServer.Services.GetService<INumberGenerator>().Generate();            

        var response = await httpClient.GetAsync("Number");
        var payload = (await response.Content.ReadAsStringAsync());

        // These values should be the same, but they are different
        Assert.NotEqual(expectedNumber.ToString(), payload);
    }
}

This is the Startup code

public class Startup
{
    // ctor and IConfiguration property

    public virtual void ConfigureServices(IServiceCollection services)
    {
        services.AddScoped<INumberGenerator, RandomNumberGenerator>();
        
        // add controllers and swagger
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        // default code, omitted for brevity 
    }
}

And this is the code for the controller

[ApiController]
[Route("[controller]")]
public class NumberController : ControllerBase
{
    private readonly INumberGenerator _numGenerator;

    public Number(INumberGenerator numGenerator) => _numGenerator = numGenerator;    

    [HttpGet]
    public int Get() => _numGenerator.Generate();
}

[davidfowl]

You can't shared the same scoped instance from the test. Each request creates a new scope. The test needs to get the instance during the request.