Testing

MessageBusTestHarness — two modes

Record-only (default): replaces IMessageBus, records everything, dispatches nothing.

var harness = services.AddMessagingTestHarness();

await sut.PlaceOrderAsync(...);          // code under test publishes

harness.HasPublished<OrderPlaced>(o => o.Total == 99m).Should().BeTrue();
harness.SentOf<ChargeCard>().Should().ContainSingle();   // point-to-point tracked separately

Dispatching: additionally delivers to the registered IMessageHandler<T> implementations and tracks per-handler outcomes. Handler failures are recorded, not rethrown — assert on Faulted instead of catching:

services.AddDispatchingTestHarness();
await using var sp = services.BuildServiceProvider();
var harness = sp.GetRequiredService<MessageBusTestHarness>();

await harness.PublishAsync(new OrderPlaced(id, 99m));

harness.HasConsumed<OrderPlaced>().Should().BeTrue();
harness.Consumed.Single().HandlerType.Should().Be(typeof(InvoiceHandler));
harness.Faulted.Should().BeEmpty();

In dispatching mode RequestAsync resolves the real IRequestHandler<TReq,TRes>, and untyped dispatch routes through the SG dispatch tables (AOT-parity with production).

Recorded	API
Published (fan-out)	Published, PublishedOf<T>(), HasPublished<T>(…)
Sent (point-to-point)	Sent, SentOf<T>(), HasSent<T>()
Consumed (per handler)	Consumed, ConsumedOf<T>(), HasConsumed<T>(…)
Faulted (per handler)	Faulted, FaultedOf<T>(), HasFaulted<T>()

Broker integration tests — Testcontainers

The Messaging test suite runs its RabbitMQ/Kafka/Azure Service Bus integration tests against real brokers started by Testcontainers (collection fixtures), so the transport paths execute in CI; when Docker itself is unavailable they degrade to skip. Reuse the fixtures as patterns:

Fixture	Starts	Notes
RabbitMqContainerFixture	rabbitmq	GetConnectionString()
KafkaContainerFixture	kafka	GetBootstrapAddress(); AdminClient topology means no pre-provisioning
AzureServiceBusContainerFixture	official ASB emulator + SQL companion	entities pre-provisioned via Config.json (AutoCreateEntities = false)

[Collection("RabbitMqBroker")]
public class MyBrokerTests(RabbitMqContainerFixture broker) { ... }

What to test where

• Handler logic → plain unit test on the handler class (no harness needed).
• “Did my code publish the right message?” → record-only harness.
• Handler wiring + fan-out + failures → dispatching harness.
• Retry/redelivery/circuit breaker → construct the SG-generated Handler.Pipeline directly (see ReliabilityPipelineSample) — the pipeline is real generated code.
• Transport semantics (DLQ, ordering, redelivery) → Testcontainers fixtures.