Test request/response

In a test scenario where a class is using the request client (IRequestClient), a request handler can be configured using the test harness to simulate a response.

In this example, a class is using the request client to check the status of an order.

Create the message contracts

using System;

public record CheckOrderStatus(Guid OrderId);

public record OrderStatus(Guid OrderId, string Status);

Create the component

A component in the application that uses the request client:

using System;
using System.Threading;
using System.Threading.Tasks;
using MassTransit;

public interface IOrderStatusChecker
{
    Task<string> GetStatus(Guid orderId, CancellationToken cancellationToken = default);
}

public class OrderStatusChecker :
    IOrderStatusChecker
{
    private readonly IRequestClient<CheckOrderStatus> _client;

    public OrderStatusChecker(IRequestClient<CheckOrderStatus> client)
    {
        _client = client;
    }

    public async Task<string> GetStatus(Guid orderId, CancellationToken cancellationToken = default)
    {
        // Send a request and await the response
        var response = await _client.GetResponse<OrderStatus>(
            new CheckOrderStatus(orderId),
            cancellationToken
        );

        return response.Message.Status;
    }
}

Create the test

To test a Request using the MassTransit Test Harness:

[Test]
public async Task Test_the_order_status_checker()
{
    await using var provider = new ServiceCollection()
        .AddMassTransitTestHarness(cfg =>
        {
            cfg.Handler<CheckOrderStatus>(async context =>
            {
                await context.RespondAsync(new OrderStatus(context.Message.OrderId, "OK"));
            });
        })
        .AddScoped<IOrderStatusChecker, OrderStatusChecker>();
        .BuildServiceProvider(true);

    var harness = await provider.StartTestHarness();

    var component = harness.Scope.ServiceProvider.GetRequiredService<IOrderStatusChecker>()

    var status = await component.GetStatus(NewId.NextGuid());

    Assert.That(status, Is.EqualTo("OK"));
}