Minimal API test config overrides only apply after app has been built

[maisiesadler]

Describe the bug

Using .net 6 minimal APIs and WebApplicationFactory for testing, the test config override is only applied after .Build.
This means any interaction with config while configuring services using builder.Configuration will be using the app configuration, not test overrides.

To Reproduce

I've created a repo that shows the difference, here is the Program, and an Example test.

Test run

Further technical details

• ASP.NET Core version: net6.0

[martincostello]

I think the problem here is that you're binding the configuration into your service while the application is still in its bootstrapping phase (which is until Build()), so the configuration isn't yet "done". It's similar to the sort of issue where you need configuration to configure other things, like if you're say using Azure Key Vault, and need to use config to configure the Key Vault provider itself.

Does it work as you'd expect if you change it to this instead?

builder.Services.AddSingleton(() => new Options(builder.Configuration["AppSettings:Options"]));

I think if you resolve it lazily like that, when the lambda to get Options runs the Configuration would then have the extra settings in it from the tests.

[maisiesadler]

Hey Martin 👋

Yep that works - this might just be a gotcha rather than a bug since the Configuration is available on builder but it's not "Done" :(
It also works using .net 6 but WebHost.CreateDefaultBuilder rather than the new WebApplication.CreateBuilder
diff
test run

[martincostello]

Yeah it's probably more of a gotcha of the new model - the WebApplicationFactory code gets invoked as part of a callback that gets called before Build() returns back to the Program class, so the code that adds your test settings won't even have run yet when you register that dependency so it can't see your overrides as they don't exist yet.

[maisiesadler]

Makes sense. Will update the code and close the issue - thanks!

[halter73]

Reopening so we document this. This might also be worth trying to fix in .NET 7. Thanks for the great repro.

[davidfowl]

@halter73 are you gonna doc this?

[kristofferjalen]

Here's my question on SO on the same issue: https://stackoverflow.com/questions/69986598/with-webapplicationfactory-add-configuration-source-before-program-cs-executes

[twinter-amosfivesix]

I stumbled upon a workaround for this issue.

If you override WebApplicationFactory<T>.CreateHost() and call IHostBuilder.ConfigureHostConfiguration() before calling base.CreateHost() the configuration you add will be visible between WebApplication.CreateBuilder() and builder.Build(). From my testing it's visible in all the various places you'd look at the config (callbacks, etc.).

I have not tried it with adding a JSON file but I imagine it should work.

Note that calling IHostBuilder.ConfigureAppConfiguration() in this manner does not work. DeferredHostBuilder treats host configuration differently from app configuration. (Code part 1 - Code part 2)

The comments in DeferredHostBuilder.ConfigureHostConfiguration actually say "We can do this for app configuration as well if it becomes necessary." Perhaps it's necessary now. 😄

(The PR that made ConfigureHostConfiguration() work like this in DeferredHostBuilder.)

Example Program

var builder = WebApplication.CreateBuilder(args);

var result = builder.Configuration["Result"];

var app = builder.Build();

app.MapGet("/", () => result);

app.Run();

public partial class Program{ }

Example appsettings.json

{
    "Result" : "Normal Result"
}

Example Test

using System.Collections.Generic;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.Testing;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using NUnit.Framework;

namespace TestProject;

[TestFixture]
public class ProgramFixture
{
    [Test]
    public async Task Should_return_override()
    {
        var factory = new MyWebApplicationFactory();

        var client = factory.CreateClient();

        var result = await client.GetStringAsync("/");

        Assert.That(result, Is.EqualTo("Override"));
    }

    private class MyWebApplicationFactory : WebApplicationFactory<Program>
    {
        protected override IHost CreateHost(IHostBuilder builder)
        {
            builder.ConfigureHostConfiguration(config =>
            {
                config.AddInMemoryCollection(new Dictionary<string, string> { { "Result", "Override" } });
            });

            // This does not work.
            //builder.ConfigureAppConfiguration(config =>
            //{
            //    config.AddInMemoryCollection(new Dictionary<string, string> { { "Result", "Override" } });
            //});

            return base.CreateHost(builder);
        }

        // This does not work.
        //protected override void ConfigureWebHost(IWebHostBuilder builder)
        //{
        //    builder.ConfigureAppConfiguration(config =>
        //    {
        //        config.AddInMemoryCollection(new Dictionary<string, string> { { "Result", "Override" } });
        //    });
        //}
    }
}