initial implementation of a github actions reporter

pkgs/test_core/lib/src/runner/configuration/reporters.dart

@@ -11,6 +11,7 @@ import '../engine.dart';
 import '../reporter.dart';
 import '../reporter/compact.dart';
 import '../reporter/expanded.dart';
+import '../reporter/github.dart';
 import '../reporter/json.dart';
 
 /// Constructs a reporter for the provided engine with the provided
@@ -43,6 +44,11 @@ final _allReporters = <String, ReporterDetails>{
           printPath: config.paths.length > 1 ||
               Directory(config.paths.single.testPath).existsSync(),
           printPlatform: config.suiteDefaults.runtimes.length > 1)),
+  'github': ReporterDetails(
+      'Custom output for Github Actions.',
+      (config, engine, sink) => GithubReporter.watch(engine, sink,
+          printPath: config.paths.length > 1 ||
+              Directory(config.paths.single.testPath).existsSync())),
   'json': ReporterDetails(
       'A machine-readable format (see '
       'https://dart.dev/go/test-docs/json_reporter.md).',
@@ -52,9 +58,11 @@ final _allReporters = <String, ReporterDetails>{
 
 final defaultReporter = inTestTests
     ? 'expanded'
-    : canUseSpecialChars
-        ? 'compact'
-        : 'expanded';
+    : githubContext
+        ? 'github'
+        : canUseSpecialChars
+            ? 'compact'
+            : 'expanded';
 
 /// **Do not call this function without express permission from the test package
 /// authors**.

pkgs/test_core/lib/src/runner/reporter/github.dart

@@ -0,0 +1,196 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore_for_file: implementation_imports
+
+import 'dart:async';
+
+import 'package:test_api/src/backend/live_test.dart';
+import 'package:test_api/src/backend/message.dart';
+import 'package:test_api/src/backend/state.dart';
+import 'package:test_api/src/backend/util/pretty_print.dart';
+
+import '../engine.dart';
+import '../load_suite.dart';
+import '../reporter.dart';
+
+/// A reporter that prints test output using formatting for Github Actions.
+///
+/// See
+/// https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions
+/// for a description of the output format, and
+/// https://github.com/dart-lang/test/issues/1415 for discussions about this
+/// implementation.
+class GithubReporter implements Reporter {
+  /// The engine used to run the tests.
+  final Engine _engine;
+
+  /// Whether the path to each test's suite should be printed.
+  final bool _printPath;
+
+  /// Whether the reporter is paused.
+  var _paused = false;
+
+  /// The set of all subscriptions to various streams.
+  final _subscriptions = <StreamSubscription>{};
+
+  final StringSink _sink;
+  final _helper = _GithubHelper();
+
+  final Map<LiveTest, List<Message>> _testMessages = {};
+
+  /// Watches the tests run by [engine] and prints their results as JSON.
+  static GithubReporter watch(
+    Engine engine,
+    StringSink sink, {
+    required bool printPath,
+  }) =>
+      GithubReporter._(engine, sink, printPath);
+
+  GithubReporter._(this._engine, this._sink, this._printPath) {
+    _subscriptions.add(_engine.onTestStarted.listen(_onTestStarted));
+    _subscriptions.add(_engine.success.asStream().listen(_onDone));
+  }
+
+  @override
+  void pause() {
+    if (_paused) return;
+    _paused = true;
+
+    for (var subscription in _subscriptions) {
+      subscription.pause();
+    }
+  }
+
+  @override
+  void resume() {
+    if (!_paused) return;
+    _paused = false;
+
+    for (var subscription in _subscriptions) {
+      subscription.resume();
+    }
+  }
+
+  void _cancel() {
+    for (var subscription in _subscriptions) {
+      subscription.cancel();
+    }
+    _subscriptions.clear();
+  }
+
+  /// A callback called when the engine begins running [liveTest].
+  void _onTestStarted(LiveTest liveTest) {
+    // Convert the future to a stream so that the subscription can be paused or
+    // canceled.
+    _subscriptions.add(
+        liveTest.onComplete.asStream().listen((_) => _onComplete(liveTest)));
+
+    // Collect messages from tests as they are emitted.
+    _subscriptions.add(liveTest.onMessage.listen((message) {
+      _testMessages.putIfAbsent(liveTest, () => []).add(message);
+    }));
+  }
+
+  /// A callback called when [liveTest] finishes running.
+  void _onComplete(LiveTest test) {
+    final errors = test.errors;
+    final messages = _testMessages[test] ?? [];
+    final skipped = test.state.result == Result.skipped;
+    final failed = errors.isNotEmpty;
+
+    void emitMessages(List<Message> messages) {
+      for (var message in messages) {
+        _sink.writeln(message.text);
+      }
+    }
+
+    void emitErrors(List<AsyncError> errors) {
+      for (var error in errors) {
+        _sink.writeln('${error.error}');
+        _sink.writeln(error.stackTrace.toString().trimRight());
+      }
+    }
+
+    final isLoadSuite = test.suite is LoadSuite;
+    if (isLoadSuite) {
+      // Don't emit any info for 'loadSuite' tests, unless they contain errors.
+      if (errors.isNotEmpty || messages.isNotEmpty) {
+        _sink.writeln('${test.suite.path}:');
+        emitMessages(messages);
+        emitErrors(errors);
+      }
+
+      return;
+    }
+
+    final prefix = failed
+        ? _GithubHelper.failedIcon
+        : skipped
+            ? _GithubHelper.skippedIcon
+            : _GithubHelper.passedIcon;
+    final statusSuffix = failed
+        ? ' (failed)'
+        : skipped
+            ? ' (skipped)'
+            : '';
+
+    var name = test.test.name;
+    if (_printPath && test.suite.path != null) {
+      name = '${test.suite.path}: $name';
+    }
+    _sink.writeln(_helper.startGroup('$prefix $name$statusSuffix'));
+    emitMessages(messages);
+    emitErrors(errors);
+    _sink.writeln(_helper.endGroup);
+  }
+
+  void _onDone(bool? success) {
+    _cancel();
+
+    _sink.writeln();
+
+    final hadFailures = _engine.failed.isNotEmpty;
+    String message =
+        '${_engine.passed.length} ${pluralize('test', _engine.passed.length)} passed';
+    if (_engine.failed.isNotEmpty) {
+      message += ', ${_engine.failed.length} failed';
+    }
+    if (_engine.skipped.isNotEmpty) {
+      message += ', ${_engine.skipped.length} skipped';
+    }
+    message += '.';
+    _sink.writeln(
+      hadFailures
+          ? _helper.error(message)
+          : '${_GithubHelper.celebrationIcon} $message',
+    );
+  }
+
+  // todo: do we need to bake in awareness about tests that haven't completed
+  // yet?
+
+  // ignore: unused_element
+  String _normalizeTestResult(LiveTest liveTest) {
+    // For backwards-compatibility, report skipped tests as successes.
+    if (liveTest.state.result == Result.skipped) return 'success';
+    // if test is still active, it was probably cancelled
+    if (_engine.active.contains(liveTest)) return 'error';
+    return liveTest.state.result.toString();
+  }
+}
+
+class _GithubHelper {
+  static const String passedIcon = '✅';
+  static const String failedIcon = '❌';
+  static const String skippedIcon = '❎';
+  static const String celebrationIcon = '🎉';
+
+  _GithubHelper();
+
+  String startGroup(String title) => '::group::${title.replaceAll('\n', ' ')}';
+  final String endGroup = '::endgroup::';
+
+  String error(String message) => '::error::$message';
+}

pkgs/test_core/lib/src/util/io.dart

@@ -87,6 +87,12 @@ final _tempDir = Platform.environment.containsKey('_UNITTEST_TEMP_DIR')
 bool get canUseSpecialChars =>
     (!Platform.isWindows || stdout.supportsAnsiEscapes) && !inTestTests;
 
+/// Detect whether we're running in a Github Actions context.
+///
+/// See
+/// https://docs.github.com/en/actions/learn-github-actions/environment-variables.
+bool get githubContext => Platform.environment['GITHUB_ACTIONS'] == 'true';
+
 /// Creates a temporary directory and returns its path.
 String createTempDir() =>
     Directory(_tempDir).createTempSync('dart_test_').resolveSymbolicLinksSync();