AG-UI .NET Integration Tests

End-to-end tests for the AG-UI .NET SDK that post RunAgentInput, stream events over the wire (SSE or protobuf), and assert behavior through the AGUIChatClient (IChatClient) abstraction.

Orientation

The canonical project layout, endpoint pattern, and naming live in sdks/dotnet/AGENTS.md (project layout + endpoint pattern) and sdks/dotnet/docs/architecture.md (the server/client pipeline). Read those first; this skill covers only the integration-test mechanics on top of them.

One durable gotcha: the test project folder and csproj are named tests/AGUI.Hosting.AspNetCore.IntegrationTests/ (kept after the server package was renamed to AGUI.Server), but all types live in namespace AGUI.Server.IntegrationTests. The ASP.NET hosting glue (AddAGUI, the negotiating endpoint, AGUIResults) lives in samples/AGUI.Samples.Shared, and the protobuf formatter comes from AGUI.Protobuf.

Project Layout

tests/AGUI.Hosting.AspNetCore.IntegrationTests/   # namespace AGUI.Server.IntegrationTests
├── Infrastructure/
│   ├── IntegrationTestBase.cs          # Two-tier base: generic <TEntryPoint> + non-generic (uses Program). Emit helpers, CollectUpdates, CreateClient(handler[, TransportFormat]), VerifyCaptures (8 capture points), recording load/save, id scrubbing.
│   ├── TransportFormat.cs              # enum { Json, Protobuf } — selects the wire encoding the test client negotiates
│   ├── DelegatingStreamingChatClient.cs # Func-based IChatClient for inline server behavior
│   ├── CapturingChatClient.cs          # IChatClient decorator that records server-side calls (ServerCallCapture)
│   ├── CapturingAGUITransport.cs       # IAGUITransport decorator that records client-side turns (TurnCapture)
│   ├── ServerCallCapture.cs            # RunAgentInput + ChatMessage[] + ChatOptions + ChatResponseUpdate[] per server call
│   ├── TurnCapture.cs                  # RunAgentInput + BaseEvent[] per client-side turn
│   ├── ChatResponseUpdateCaptureConverter.cs # JsonConverter that renders ChatResponseUpdate (+RawRepresentation) for snapshots
│   ├── AGUIEndpointExtensions.cs       # Test-local MapAGUI: ToChatRequestContext + AsAGUIEventStreamAsync, returns AGUIResults.Events (negotiating)
│   ├── AGUIServerSentEventsResult.cs   # Legacy SSE-only IResult (still present; the live endpoint uses AGUIResults instead)
│   ├── AGUICapabilitiesEndpointRouteBuilderExtensions.cs # Test-only AgentCapabilities publisher (the SDK ships no capabilities endpoint; the spec doesn't define one)
│   ├── Program.cs                      # Minimal host: AddAGUI() + register ProtobufEventStreamFormatter + DelegatingStreamingChatClient + MapAGUI("/agui")
│   └── VerifyConfig.cs                 # ModuleInitializer for Verify settings (DontScrubDateTimes, DiffRunner disabled)
├── RunLifecycleIntegrationTest.cs      # Run lifecycle events            [Theory Json/Protobuf]
├── TextStreamingIntegrationTest.cs     # Text streaming + multi-turn     [Theory Json/Protobuf]
├── ToolCallIntegrationTest.cs          # Tool call events                [Theory + one Json-only ToolCallResult fact]
├── ClientToolIntegrationTest.cs        # Client (frontend) tools          [Theory Json/Protobuf]
├── MixedToolInvocationIntegrationTest.cs # Mixed server+client tool batches (approval-flow) [Json-only, has Verify baselines]
├── FrontendToolReinvocationTest.cs     # Frontend tool re-invocation      [Json-only]
├── StateManagementIntegrationTest.cs   # State snapshot/delta             [Theory Json/Protobuf]
├── ReasoningIntegrationTest.cs         # Thinking/reasoning events        [Json-only]
├── ActivityIntegrationTest.cs          # Activity snapshot/delta          [Json-only]
├── CustomAndRawEventIntegrationTest.cs # Custom/raw events                [Theory Json/Protobuf]
├── RawRepresentationFactoryIntegrationTest.cs # Custom RawRepresentation factory [Theory Json/Protobuf]
├── CapabilitiesEndpointIntegrationTest.cs # Capabilities endpoint (exercises the test-local helper) [Json-only]
├── TransportEquivalenceIntegrationTest.cs # Asserts Json and Protobuf decode to identical ChatResponseUpdate sequences
├── AGUIResultsTest.cs                  # Accept-header negotiation (proto vs SSE vs 406) for AGUIResults.Events
├── Samples/GettingStarted/
│   ├── StepNN_XyzTest.cs               # Replay/snapshot test per sample (Step01..Step12)
│   ├── fixtures/{Sample}/*.recording.json   # Recorded List<List<ChatResponseUpdate>> (one list per turn)
│   └── baselines/{Sample}/*.verified.json   # Verify snapshots, one file per capture point (see below)
└── AGUI.Hosting.AspNetCore.IntegrationTests.csproj  # references AGUI.Client, AGUI.Protobuf, AGUI.Samples.Shared + every Step01..Step12 Client/Server

Architecture

IChatClient-based design

The server side always works with ChatResponseUpdate streams. The AG-UI hosting layer converts these to BaseEvent streams on the wire (SSE or protobuf). Tests verify behavior at the ChatResponseUpdate level, inspecting the underlying AG-UI event via update.RawRepresentation.

DelegatingStreamingChatClient pattern

Define server behavior inline via a Func<IEnumerable<ChatMessage>, ChatOptions?, CancellationToken, IAsyncEnumerable<ChatResponseUpdate>>:

var client = CreateClient((messages, options, ct) =>
    EmitTextResponse("Hello!", ct), format);

CreateClient builds a fresh AGUIChatClient over a WebApplicationFactory<Program> HTTP pipeline with DelegatingStreamingChatClient injected via ConfigureTestServices.

Two-tier base class

• IntegrationTestBase<TEntryPoint> — generic base for any Program. Provides CollectUpdates, ExtractText, the Emit* helpers, VerifyCaptures, recording load/save, and snapshot id scrubbing.
• IntegrationTestBase — non-generic subclass of IntegrationTestBase<Program>. Sets the .slnx content-root env var and exposes the CreateClient overloads that inject DelegatingStreamingChatClient.

Host registration

Infrastructure/Program.cs registers the protobuf formatter so the server can answer either transport:

builder.Services.AddAGUI();                                                       // AGUI.Samples.Shared
builder.Services.AddSingleton<IAGUIEventStreamFormatter, ProtobufEventStreamFormatter>(); // AGUI.Protobuf

The test endpoint mirrors the production shape but returns the negotiating result:

var events = chatClient.GetStreamingResponseAsync(ctx.Messages, ctx.ChatOptions, ct)
    .AsAGUIEventStreamAsync(ctx, ct);
return AGUIResults.Events(events, httpContext, ct);   // negotiates protobuf vs SSE from Accept

Emit helpers

All Emit* helpers yield ChatResponseUpdate (never BaseEvent); the pipeline converts them. They take a trailing [EnumeratorCancellation] CancellationToken ct = default:

• EmitTextResponse(text, ct) — assistant TextContent
• EmitToolCallResponse(callId, name, args, ct) — FunctionCallContent, FinishReason = ToolCalls
• EmitToolCallWithResultResponse(callId, name, args, result, ct) — call update then a FunctionResultContent update
• EmitEmptyResponse(ct) — yields nothing

Transport parameterization (Json / Protobuf)

Most event-shape tests are [Theory] over TransportFormat:

[Theory]
[InlineData(TransportFormat.Json)]
[InlineData(TransportFormat.Protobuf)]
public async Task PostRun_TextContent_MapsToTextMessageEvents(TransportFormat format)
{
    var client = CreateClient((messages, options, ct) =>
        EmitTextResponse("Hello world!", ct), format);
    var updates = await CollectUpdates(client, [new ChatMessage(ChatRole.User, "Hi")]);
    // ...assert via update.RawRepresentation...
}

How CreateClient(handler, format) works:

• TransportFormat.Json → default SSE transport (text/event-stream); no negotiation handler.
• TransportFormat.Protobuf → inserts an AGUIEventStreamHandler advertising [protobuf, sse] (ProtobufEventStreamFormatter + SseEventStreamFormatter) into the client HttpClient pipeline, so the request prefers application/vnd.ag-ui.event+proto and the response is decoded accordingly.

Assertions and Verify baselines are reused unchanged across both formats. Capture happens at the decoded event/ChatResponseUpdate layer, and the request is always JSON, so only the wire encoding differs. TransportEquivalenceIntegrationTest pins this invariant by running the same scenario over both formats and asserting the decoded update sequences are identical.

Intentionally Json-only tests

A few suites are plain [Fact] (Json only) because their events are not representable in the protobuf subset — encoding them would throw NotSupportedException:

• ReasoningIntegrationTest (thinking/reasoning), ActivityIntegrationTest (activity snapshot/delta).
• The ToolCallResult scenario in ToolCallIntegrationTest (FunctionResultContent → TOOL_CALL_RESULT, a .NET-only event). The rest of that file stays [Theory].
• MixedToolInvocationIntegrationTest, FrontendToolReinvocationTest, and CapabilitiesEndpointIntegrationTest are also Json-only.

When you add a [Theory] test, prefer parameterizing over TransportFormat. Only fall back to a Json-only [Fact] when the scenario emits a .NET-only event with no proto representation — and add a one-line comment saying so.

Procedure: writing a new integration test

1. Pick the file by event category (see layout table). New category → {Category}IntegrationTest.cs : IntegrationTestBase.
2. Declare the class with the WebApplicationFactory<Program> ctor:

   public sealed class MyFeatureIntegrationTest : IntegrationTestBase
   {
       public MyFeatureIntegrationTest(WebApplicationFactory<Program> factory) : base(factory) { }
   }
   

3. Write a [Theory] over TransportFormat (or [Fact] if Json-only per above), call CreateClient(handler, format), drive a turn with CollectUpdates, and assert the event sequence with Assert.Collection, checking u.RawRepresentation types/properties.
4. Multi-turn: enqueue handlers in a Queue<Func<...>> and dequeue per call; pass the full message history (prior user + synthesized assistant messages) on later turns.
5. Tool calls: pass tools via ChatOptions { Tools = [DummyClientTool] } (DummyClientTool is built with CreateToolDeclaration).
6. New reusable emitter → add it to IntegrationTestBase.cs; yield ChatResponseUpdate, not BaseEvent.

[Theory]
[InlineData(TransportFormat.Json)]
[InlineData(TransportFormat.Protobuf)]
public async Task PostRun_FunctionCallContent_MapsToToolCallEvents(TransportFormat format)
{
    var client = CreateClient((messages, options, ct) =>
        EmitToolCallResponse("call-1", "get_weather",
            new Dictionary<string, object?> { ["location"] = "Seattle" }, ct), format);

    var updates = await CollectUpdates(client,
        [new ChatMessage(ChatRole.User, "Hi")],
        new ChatOptions { Tools = [DummyClientTool] });

    Assert.Collection(updates,
        u => Assert.IsType<RunStartedEvent>(u.RawRepresentation),
        u =>
        {
            var fcc = Assert.Single(u.Contents.OfType<FunctionCallContent>());
            Assert.Equal("get_weather", fcc.Name);
            Assert.Equal("call-1", fcc.CallId);
        },
        u => Assert.Equal(ChatFinishReason.ToolCalls, u.FinishReason));
}

Sample recording / replay tests

Samples/GettingStarted/StepNN_XyzTest.cs runs each sample as a real host and verifies the full MEAI↔AG-UI round-trip deterministically. Samples exist for Step01–Step13 (Step12 = parallel tool calls, Step13 = protobuf); replay tests currently cover Step01–Step12 plus MixedToolInvocation.

Key types

• FakeChatClient — defined per sample server project (e.g. Step01_GettingStarted.Server), a Queue-of-handlers IChatClient used in replay mode.
• CapturingChatClient — wraps the real/fake server IChatClient, records each call as a ServerCallCapture (RunAgentInput, messages, options, updates).
• CapturingAGUITransport — wraps IAGUITransport, records each SendAsync as a TurnCapture (RunAgentInput + emitted BaseEvents).

Pattern

Each test inherits IntegrationTestBase<StepNN_Xyz.Server.Program> and uses a local CreateCapturingClient:

public sealed class Step01_GettingStartedTest
    : IntegrationTestBase<Step01_GettingStarted.Server.Program>
{
    [Fact]
    public async Task PostRun_MultiTurn_SynthesizesAssistantMessages()
    {
        var (aguiClient, transport, server) = CreateCapturingClient(turnCount: 2);
        var clientMessages = new List<List<ChatMessage>>();
        var clientUpdates = new List<List<ChatResponseUpdate>>();

        await SampleClient.RunAsync(aguiClient, TextWriter.Null, clientMessages, clientUpdates);

        await VerifyAllCaptures(transport, server, clientMessages, clientUpdates);
    }
}

• Replay vs record: CreateCapturingClient calls LoadRecording(testName). If a fixture exists it injects a FakeChatClient replaying it; otherwise it wraps the app's real IChatClient and SaveRecording writes a fresh fixture.
• Fixtures: Samples/GettingStarted/fixtures/{Sample}/{TestMethod}.recording.json — a serialized List<List<ChatResponseUpdate>> (one inner list per turn).

The 8 capture points (baselines)

VerifyCaptures writes one Verify target per capture point per turn under Samples/GettingStarted/baselines/{Sample}/, named {TestMethod}#Turn_{NN}.{CC}.{Request|Response}.{Client|Server}.{AGUI|NET}.verified.json. The eight points trace the full round-trip in order:

Volatile ids (call_, msg_, run_, GUIDs, …) are scrubbed to stable *_Id_N placeholders, and createdAt/totalTokenCount are stripped, so baselines are deterministic. Because capture is at the decoded layer, the same baselines hold for protobuf runs.

Updating baselines

When a snapshot changes, review the .received.json diff, then accept (e.g. dotnet test --environment VERIFY_ACCEPT=true). When adding a sample test, the first record-mode run generates both the fixture and the baselines — review them before committing.

Key rules

1. Parameterize over TransportFormat with [Theory]/[InlineData] unless the events are .NET-only (then [Fact] + comment).
2. Assert.Collection for event sequences — validates count, order, and properties together.
3. Assert on u.RawRepresentation to inspect the underlying AG-UI event; emit helpers yield ChatResponseUpdate, not BaseEvent.
4. CreateClient returns AGUIChatClient (not HttpClient); drive turns with CollectUpdates.
5. No agent classes — use DelegatingStreamingChatClient + inline handler; multi-turn uses a Queue<Func<...>>.
6. The pipeline wraps RunStarted/RunFinished — emit helpers don't produce lifecycle events.
7. One test file per event category; name {Category}IntegrationTest.cs.
8. Sample tests inherit IntegrationTestBase<StepNN_Xyz.Server.Program>, use CreateCapturingClient (record/replay), and verify all 8 capture points via VerifyCaptures.
9. Use current names: package AGUI.Server, namespace AGUI.Server.IntegrationTests, ASP.NET glue (AGUIResults, AddAGUI) from AGUI.Samples.Shared.

Build & run

From sdks/dotnet/:

dotnet test tests/AGUI.Hosting.AspNetCore.IntegrationTests/