Testing & Tooling

Testing RPC services should be as frictionless as testing regular functions. RPC Dart exposes utilities and patterns that make it simple to exercise contracts, transports, and streaming logic in isolation or end-to-end.

In-memory end-to-end tests

RpcInMemoryTransport.pair() produces a connected client/server transport with zero serialisation overhead. It is the quickest way to run integration tests.

final (clientTransport, serverTransport) = RpcInMemoryTransport.pair();

final responder = RpcResponderEndpoint(transport: serverTransport)
  ..registerServiceContract(CalculatorResponder())
  ..start();

final caller = RpcCallerEndpoint(transport: clientTransport);
final calculator = CalculatorCaller(caller);

expect(await calculator.add(AddRequest(1, 2)), isA<AddResponse>());

Because data is passed by reference you can assert on complex object identity or mutations without dealing with serialisation noise.

Controlling context during tests

RpcContextBuilder helps you craft trace IDs, deadlines, and metadata for your scenarios:

final ctx = RpcContextBuilder()
    .withHeader('x-test-case', 'retry-path')
    .withTimeout(const Duration(milliseconds: 200))
    .build();

await calculator.add(AddRequest(1, 2), context: ctx);

Use RpcContext.sanitize before snapshotting contexts in golden tests to strip sensitive headers such as API keys.

Inspecting transport state

Expose RpcEndpointHealth in assertions to guarantee transports remain healthy throughout the test:

final report = await caller.health();
expect(report.endpointStatus.level, RpcHealthLevel.healthy);
expect(report.transportStatus?.details['activeStreams'], equals(0));

Pair this with caller.ping() when you need deterministic latency expectations or to verify that routers point to the right downstream service.

Testing streaming behaviour

Streams are first-class citizens in the testing story. Use expectLater with the Dart Stream API to assert on emitted events, errors, and completion:

final updates = chat.joinRoom('general', 'u-1');
expectLater(
  updates,
  emitsInOrder([
    predicate<ChatMessage>((m) => m.type == MessageType.joined),
    emitsDone,
  ]),
);

StreamDistributor provides metrics that you can assert against to confirm that cleanup logic works as expected:

final distributor = StreamDistributor<ChatMessage>();
final stream = distributor.createClientStreamWithId('test');
final subscription = stream.listen((_) {});

distributor.publish(ChatMessage('hello'));
expect(distributor.metrics.totalMessages, 1);
await subscription.cancel();

Faking transports

When you need to simulate edge cases (packet loss, reconnection, buffering) extend RpcBaseTransport in tests. The base class already handles stream ID management and incoming message dispatch, so you only implement the behaviour under test.

class FlakyTransport extends RpcBaseTransport {
  FlakyTransport() : super(isClient: true);

  bool dropNextMessage = false;

  @override
  Future<void> sendMessage(int streamId, Uint8List data, {bool endStream = false}) async {
    if (dropNextMessage) {
      dropNextMessage = false;
      return; // simulate packet loss
    }
    addIncomingMessage(RpcTransportMessage.withPayload(
      payload: data,
      streamId: streamId,
      isEndOfStream: endStream,
    ));
  }

  @override
  Future<void> sendMetadata(int streamId, RpcMetadata metadata, {bool endStream = false}) async {}

  @override
  Future<void> finishSending(int streamId) async {}
}

Combine flaky transports with the real endpoints to exercise retry logic and error handling paths.

Leveraging logging in tests

Inject a custom logger via RpcLogger.setLoggerFactory that records messages in memory. This lets you assert on emitted diagnostics without relying on stdout.

final events = <String>[];
RpcLogger.setLoggerFactory((name, {colors, label, context}) {
  return InMemoryLogger(name, onLog: events.add);
});

Automation tips

• Add a just recipe or dart test --platform vm command to CI that runs your suites with --run-skipped to surface quarantined tests early.
• Run dart run benchmark/benchmark.dart inside packages/rpc_dart to stress-test zero-copy code paths and compare codec performance.
• Capture RpcContext snapshots on failure to speed up debugging of distributed workflows.

With these patterns your RPC services stay easy to verify, refactor, and extend as new requirements arrive.