Configure AspNetCore TestServer to return 500 instead of throwing exception

Question

I am developing a Web API that in some cases will respond with 500 (ugly design, I know, but can't do anything about it). In tests there's an ApiFixture that contains AspNetCore.TestHost:

public class ApiFixture
{
    public TestServer ApiServer { get; }
    public HttpClient HttpClient { get; }

    public ApiFixture()
    {
        var config = new ConfigurationBuilder()
            .AddEnvironmentVariables()
            .Build();

        var path = Assembly.GetAssembly(typeof(ApiFixture)).Location;
        var hostBuilder = new WebHostBuilder()
            .UseContentRoot(Path.GetDirectoryName(path))
            .UseConfiguration(config)
            .UseStartup<Startup>();

        ApiServer = new TestServer(hostBuilder);
        HttpClient = ApiServer.CreateClient();
    }
}

When I am calling API endpoint with HttpClient from this fixture it should respond with 500, instead I am getting exception that is being raised in the tested controller. I know that in tests it might be a nice feature, but I don't want that - I want to test actual behavior of controller, which is returning internal server error. Is there a way to reconfigure TestServer to return response?

Code in controller action is irrelevant, can be throw new Exception();

Answer 1

You can create an exception handling middleware and use it in tests or better always

public class ExceptionMiddleware
{
    private readonly RequestDelegate next;

    public ExceptionMiddleware(RequestDelegate next)
    {
        this.next = next;
    }

    public async Task Invoke(HttpContext httpContext)
    {
        try
        {
            await this.next(httpContext);
        }
        catch (Exception ex)
        {
            httpContext.Response.ContentType = MediaTypeNames.Text.Plain;
            httpContext.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
            await httpContext.Response.WriteAsync("Internal server error!");
        }
    }
}

Now you can register this middleware in your Startup.cs:

...
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseMiddleware<ExceptionMiddleware>();
    ...
    app.UseMvc();
}

And if you don't want to use it all the time you can create TestStartup - a child class of your Startup and override Configure method to call UseMiddleware only there. Then you will need to use the new TestStartup class in the tests only.