New test features for the holidays!

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Natalie Weizenbaum

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Dec 20, 2016, 9:35:44 PM12/20/16

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Hey Dartisans,

I've just released test 0.12.18, which adds a couple features that I think are pretty neat.

First up is addTearDown(), which allows you to add tear-down callbacks from within a test. Like with tearDown(), they'll run even if the test fails. This is particularly useful for writing testing libraries—for example:

/// Creates a temporary directory that will be deleted when
/// the test finishes running.
String createSandbox([String prefix]) {
  prefix ??= 'dart';
  var sandbox = Directory.systemTemp
      .createTempSync('${prefix}_').path;

  // Delete [sandbox] when the test finishes running.
  addTearDown(() {
    new Directory(sandbox).deleteSync(recursive: true);
  });

  return sandbox;
}

The second feature is actually a pair of functions: spawnHybridUri() and spawnHybridCode(). These allow browser tests to spawn isolates that run on the Dart VM—either from a well-known URI, or from a chunk of inline Dart code. I've personally needed this before for testing packages like web_socket_channel, who run in the browser and whose whole point is to communicate with a server. It could also be used for running tests against a server-side app, or for something I haven't even dreamed of. For example:

void main() {
  int port;
  setUp(() async {
    var channel = spawnHybridCode(r"""
      import 'dart:io';

      import 'package:stream_channel/stream_channel.dart';

      hybridMain(StreamChannel channel) async {
        var server = await HttpServer.bind('localhost', 0);
        server.transform(new WebSocketTransformer())
            .listen((webSocket) {
          webSocket.listen((request) {
            webSocket.add(request);
          });
        });
        channel.sink.add(server.port);
      }
    """, stayAlive: true);

    port = await channel.stream.first;
  });

  test("communicates with the server", () async {
    channel = new HtmlWebSocketChannel.connect(
        "ws://localhost:$port");

    var queue = new StreamQueue(channel.stream);
    channel.sink.add("foo");
    expect(await queue.next, equals("foo"));
  });
}