Testing from JavaScript

[James Duley (parched)]

Currently, I'm successfully testing my API and everything behind it using a C# test project with DistributedApplicationTestingBuilder.

I would now like to include the JavaScript frontend in that loop to get a full end-to-end test. The frontend is written in TypeScript. Does something like DistributedApplicationTestingBuilder exist for Node.js? If not, how would I do it manually?

I can start the app host by launching a dotnet run process.
However, I can't see how to get the API endpoint, the stdout just has the dashboard URL.
I tried running dotnet run -- --help to see what arguments the app host accepts, but it ignored --help, is this documented somewhere?

[Mohcine FAKIRI (MohcineDev)]

Hi
what do you mean by "can't see how to get the API endpoint" did you create the application your self?

[James Duley (parched)]

Yes, I mean the asp.net core project defined in the app host, I need to know the port it's running. I guess i could get the node js process to choose a random port then set an env var to tell the apphost to hardcode it Is there a better way?

[Mohcine FAKIRI (MohcineDev)]

I got you an AI answer and i hope it helps without the hard code:

1. The Right Way to Get Service Endpoints

The way .NET Aspire manages ports is dynamic—it assigns them when the application starts. Trying to hardcode the port in your frontend is brittle and will break if you run other Aspire apps simultaneously.

The correct way to get the API endpoint in your end-to-end test is to use the DistributedApplicationTestingBuilder before you launch your Node.js process.

The DistributedApplicationTestingBuilder gives you access to the running application's services. You can start the app host, query the endpoint for the specific service (your ASP.NET Core API), and then pass that endpoint URL to your frontend test runner as an environment variable.

Here's the pattern in C#:

// Inside your C# test setup (e.g., in a TestFixture or XUnit collection setup)
await using var appHost = await DistributedApplicationTestingBuilder.CreateAsync<Projects.AppHost>();

// 1. Start the application host
await appHost.StartAsync();

// 2. Get the actual endpoint URL for your API service
var apiServiceEndpoint = appHost.Get  
  // Replace "api-service-name" with the name you used in your AppHost project (e.g., "webapi")
  .Get  
  .GetResource(resourceName: "api-service-name") 
  .Get  
  .GetEndpoints() 
  .Single(e => e.Name == "http") // or "https" if you prefer
  .Uri;

// 3. Now, launch your Node.js test process, passing the URL as an environment variable
// e.g., Environment.SetEnvironmentVariable("API_BASE_URL", apiServiceEndpoint);
// And then start your Node.js E2E test runner (e.g., Playwright, Cypress, etc.)
// Make sure to clean up by calling appHost.StopAsync() when done.