Test a saga state machine

To test a saga state machine using the MassTransit Test Harness:

[Test]
public async Task ASampleTest()
{
    await using var provider = new ServiceCollection()
        .AddMassTransitTestHarness(cfg =>
        {
            cfg.AddSagaStateMachine<OrderStateMachine, OrderState>();
        })
        .BuildServiceProvider(true);

    var harness = provider.GetRequiredService<ITestHarness>();

    await harness.Start();

    var sagaId = Guid.NewGuid();
    var orderNumber = "ORDER123";

    await harness.Bus.Publish(new OrderSubmitted
    {
        CorrelationId = sagaId,
        OrderNumber = orderNumber
    });

    Assert.That(await harness.Consumed.Any<OrderSubmitted>());

    var sagaHarness = harness.GetSagaStateMachineHarness<OrderStateMachine, OrderState>();

    Assert.That(await sagaHarness.Consumed.Any<OrderSubmitted>());

    Assert.That(await sagaHarness.Created.Any(x => x.CorrelationId == sagaId));

    var instance = sagaHarness.Created.ContainsInState(sagaId, sagaHarness.StateMachine, sagaHarness.StateMachine.Submitted);
    Assert.IsNotNull(instance, "Saga instance not found");
    Assert.That(instance.OrderNumber, Is.EqualTo(orderNumber));

    Assert.IsTrue(await harness.Published.Any<OrderApprovalRequired>());

    // test side effects of OrderState here
}