AG-UI .NET Unit Tests

Conventions for the tests/*.UnitTests projects. Mined from sdks/dotnet/AGENTS.md and existing tests. An agent gets these wrong by default: asserting on deserialized objects (misses naming bugs), comparing full JSON strings (fragile), using reflection, or skipping the FixtureLoader compatibility pattern.

All commands run from sdks/dotnet/.

Unit-test projects

Run one project: dotnet test tests/AGUI.Abstractions.UnitTests/

Conventions

• Test files live directly under the project root (not mirrored into Events/ subfolders). Compatibility tests go in the Compatibility/ subfolder.
• Test class name: {TypeUnderTest}Test (RunStartedEventTest, ToolCallBuilderTest). Compatibility class: {Category}CompatibilityTest (RunEventsCompatibilityTest).
• public sealed class, one class per file, file name matches type.
• [Fact] for single cases, [Theory] + [InlineData] for parameterized cases.
• Serialize via the source-generated context: AGUIJsonSerializerContext.Default.{Type} — never JsonSerializer.Serialize<object>(...) or hand-rolled options.

Pattern 1 — Event serialization round-trip (Abstractions)

Serialize via the source-gen context, parse with JsonDocument, assert each camelCase property name AND the type discriminator. This is what catches [JsonPropertyName] bugs.

[Fact]
public void Serialization_RoundTrips()
{
    var evt = new RunStartedEvent { ThreadId = "t1", RunId = "r1", Timestamp = 1234567890 };

    var json = JsonSerializer.Serialize(evt, AGUIJsonSerializerContext.Default.RunStartedEvent);
    using var doc = JsonDocument.Parse(json);

    Assert.Equal("RUN_STARTED", doc.RootElement.GetProperty("type").GetString());
    Assert.Equal("t1", doc.RootElement.GetProperty("threadId").GetString());
    Assert.Equal("r1", doc.RootElement.GetProperty("runId").GetString());
    Assert.Equal(1234567890, doc.RootElement.GetProperty("timestamp").GetInt64());
}

Pattern 2 — Backward-compatibility fixtures (Abstractions/Compatibility)

Compatibility/Fixtures/*.json are produced by the TypeScript reference implementation. Deserialize them into .NET types and assert the values — this catches wire-format drift. Load arrays with FixtureLoader; write one test method per event shape.

public sealed class RunEventsCompatibilityTest
{
    private readonly JsonElement[] _fixtures = FixtureLoader.LoadFixture("run-events.json");

    [Fact]
    public void RunStartedEvent_DeserializesFromTypeScriptPayload()
    {
        var evt = FixtureLoader.DeserializeAsBaseEvent(_fixtures[0]);

        var typed = Assert.IsType<RunStartedEvent>(evt);
        Assert.Equal("thread-1234", typed.ThreadId);
        Assert.Equal("run-5678", typed.RunId);
    }
}

Adding a fixture: place the TS-produced JSON array under Compatibility/Fixtures/ (embedded resource), then index into the loaded array per shape.

Pattern 3 — Protobuf codec round-trip (Protobuf)

Encode→decode and assert typed values. Compare JsonElement payloads with JsonTestHelpers.AssertEqual (deep-equals), not string compare. ProtoValueConverter tests verify JsonElement↔Value for each ValueKind.

var result = RoundTrip(new RunStartedEvent { ThreadId = "thread-1", RunId = "run-1" });
Assert.Equal("thread-1", result.ThreadId);
JsonTestHelpers.AssertEqual(expectedElement, result.RawEvent!.Value);

Pattern 4 — Client builders / handler (Client)

Drive the builder/handler through its real API and assert the produced MEAI types. ToolCallBuilder/TextMessageBuilder: feed events, flush, assert FunctionCallContent, ConversationId, ResponseId. AGUIEventStreamHandler: assert content-negotiation Accept header ordering via a test inner handler. Standard xunit assertions.

Pattern 5 — Server conversion (Server)

Convert a ChatResponseUpdate stream to AG-UI events and assert the sequence with Assert.Collection, type-checking each event and its fields (e.g. run lifecycle wraps content with RunStartedEvent/RunFinishedEvent).

Pattern 6 — SSE formatter (Formatting)

Assert MediaType, CanRead(contentType) (use [Theory]/[InlineData] for case and null/empty handling), and that WriteAsync produces the data: {json} shape per event.

❌ Critical anti-patterns

1. Never assert only on the deserialized object for serialization tests. Round-trip through your own type hides [JsonPropertyName] mistakes. Parse the JSON with JsonDocument and assert the literal camelCase property names + type discriminator.
2. Never compare full JSON strings — fragile against property ordering/whitespace. Parse and check individual properties (or JsonTestHelpers.AssertEqual for payloads).
3. Never use reflection to enumerate types or verify membership. Write explicit per-type / per-shape tests.
4. Never use ad-hoc serializer options. Serialize through AGUIJsonSerializerContext.Default.{Type} so tests exercise the real AOT context.
5. Never collapse compatibility shapes into one loop-only assertion. Keep one test method per event shape so a drift failure names the exact event.