Make it eaiser to see Application state in tests when debugging DistributedApplicationTestingBuilder

[afscrome]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

Currently if you are trying to troubleshoot an application state issue in tests run with DistributedApplicationTestingBuilder, you have limited information available around the current state of the application (e.g. has one of my resources died early).

Describe the solution you'd like

One option could be to do something with a DebuggerTypeProxy to provide a view similar to the Resources view on the Aspire dashboard. You could then hover over the app variable to get some of the information you'd otherwise get from the dashboard.

await using var app = await appHost.BuildAsync();
await app.StartAsync();

Another aid could be to add a WithDashboard method to DistributedApplicationTestingBuilder. When this is specified, the dashboard would be spun up allowing you to use the data on the dashboard for debugging. (Although this could get awkward quickly if the dashboard freezes whenever the debugger for the test is paused)

Additional context

Note, these suggestions only help with local dev when you can hook up a debugger. These don't help with debugging in CI systems (unless you can repro the same issue locally and debug there).

[davidfowl]

@JamesNK thoughts?

[afscrome]

I've been playing around with the following hand in hand with #7012 & #7039. In my experiments, I can't implement it fully as a debugger proxy as it requires subscribing to ResourceNotificationService before the app starts (which is likely before the debugger proxy is initalised), but I think that could be worked around.

internal class DistributedApplicationProxy : IDisposable
{
    // TODO: doesn't handle replicas
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    private readonly Dictionary<IResource, ResourceState> _resourceSnapshots = new();

    public IResourceCollection Resources { get; private set; }

    public DistributedApplicationProxy(DistributedApplication app)
    {
        Resources = app.Services.GetRequiredService<DistributedApplicationModel>().Resources;
        _resourceSnapshots = Resources.ToDictionary(k => k, v => new ResourceState(v));
        var resourceNotificationService = app.Services.GetRequiredService<ResourceNotificationService>();

        _ = Task.Run(async () =>
        {
            await foreach (var evt in resourceNotificationService.WatchAsync(default))
            {
                _resourceSnapshots[evt.Resource].Snapshot = evt.Snapshot;
            }

        });
    }

    internal ICollection<ResourceState> ResourceStates => _resourceSnapshots.Values;

    [DebuggerDisplay("{Snapshot}", Name ="{Resource.Name}")]
    internal class ResourceState(IResource resource)
    {
        [DebuggerBrowsable(DebuggerBrowsableState.Never)]
        public IResource Resource => resource;

        [DebuggerBrowsable(DebuggerBrowsableState.RootHidden)]
        public CustomResourceSnapshot? Snapshot { get; set; }
    }
}