Testing Event-Driven Code

Test event-driven code by subscribing before the run, capturing the events you care about, and asserting on event types and correlation ids.

Capture Events

var events = new List<AgentEvent>();

using var subscription = agent.SubscribeAny(evt =>
{
    events.Add(evt);
});

await agent.RunAsync("Summarize this branch.");

Assert.Contains(events, evt => evt is MessageTurnStartedEvent);
Assert.Contains(events, evt => evt is MessageTurnFinishedEvent);

Subscribe before RunAsync(...). Disposing the subscription stops capture.

Assert Tool Flow

var toolEvents = events
    .OfType<ToolCallStartEvent>()
    .ToList();

var search = Assert.Single(toolEvents, evt => evt.Name == "search_documents");

Assert.Contains(events.OfType<ToolCallEndEvent>(), evt => evt.CallId == search.CallId);

Use CallId to connect tool start, args, result, and end events.

Assert Custom Events

var progress = events.OfType<RetrievalProgressEvent>().ToList();

Assert.NotEmpty(progress);
Assert.All(progress, evt => Assert.Equal("refund policy", evt.Query));

For custom events that cross a hosted or persisted boundary, add a serializer round-trip test:

var json = AgentEventSerializer.ToJson(
    new RetrievalProgressEvent("refund policy", 12, 3));

var roundTripped = Assert.IsType<RetrievalProgressEvent>(
    AgentEventSerializer.FromJson(json));

Assert.Equal(3, roundTripped.DocumentsMatched);

Assert Bidirectional Flows

For request/response flows, subscribe to the request event and respond inside the handler:

using var permission = agent.Subscribe<PermissionRequestEvent>(request =>
{
    return agent.RespondAsync(new PermissionResponseEvent(
        PermissionId: request.PermissionId,
        SourceName: request.SourceName,
        Approved: true));
});

await agent.RunAsync("Use the file tool if needed.");

Then assert the resulting observability events or final output.

Keep Tests Stable

Prefer assertions on:

• event type
• CallId
• request id such as PermissionId
• MessageId
• custom event payload fields

Avoid relying on exact global ordering across unrelated event families unless the behavior under test requires it. Model output, tool calls, retries, and diagnostics may interleave differently across providers or middleware.

Related Pages

• Streaming Events
• Tool And Function Events
• Bidirectional Events
• Custom Events