dart_node_ws: Add actual WebSocket server/client interaction tests

[MelbourneDeveloper]

Problem

packages/dart_node_ws/test/ws_test.dart has a literal TODO comment on line 11:

//TODO: we need actual web socket server/client interaction tests here.

The existing tests only cover:

• WebSocketReadyState enum values (connecting=0, open=1, closing=2, closed=3)
• createWebSocketServer basic instantiation (port assignment, close callback)
• onConnection handler registration (no actual connection)

Zero tests for: message sending, message receiving, close events, error handling, JSON messaging, or any real client↔server interaction.

What's Needed

The dart_node_ws package needs actual interaction tests that verify:

• Client connects to server and server receives the connection
• Client sends a message and server receives it
• Server sends a message and client receives it
• JSON message round-trip (sendJson / onMessage parsing)
• Client close triggers server close event with code/reason
• Server close triggers client close event
• Error handler fires on connection errors
• Multiple concurrent clients

A test_server.dart helper already exists at packages/dart_node_ws/test/test_server.dart with echo/JSON support that could be leveraged.

CI Coverage Consideration

The CI workflow (.github/workflows/ci.yml via tools/test.sh) runs dart_node_ws tests as a Tier 2 Node package. Currently this only exercises the shallow unit tests above.

However, other test suites already use dart_node_ws as part of integration tests:

• examples/backend/ runs a WebSocketService that uses dart_node_ws for real-time task broadcasting
• examples/frontend/test/web_app_test.dart tests WebSocket-driven UI updates (via mocked browser WebSocket)

These integration tests in other packages should count toward dart_node_ws coverage in CI. The CI pipeline should be updated to aggregate coverage from downstream consumers that exercise dart_node_ws code paths, not just the package's own test directory.

References

• packages/dart_node_ws/test/ws_test.dart - current tests (line 11 TODO)
• packages/dart_node_ws/test/test_server.dart - existing test server helper
• packages/dart_node_ws/lib/src/websocket_types.dart - types/API surface to test
• packages/dart_node_ws/lib/src/websocket_server.dart - server factory to test
• examples/backend/lib/services/websocket_service.dart - real-world usage
• tools/test.sh - CI test runner