Add some basic interfaces that will be used for the test runner.

lib/src/live_test_controller.dart

Index: lib/src/live_test_controller.dart
diff --git a/lib/src/live_test_controller.dart b/lib/src/live_test_controller.dart
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+++ b/lib/src/live_test_controller.dart
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+// Copyright (c) 2015, 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.
+
+library unittest.live_test_controller;
+
+import 'dart:async';
+import 'dart:collection';
+
+import 'package:stack_trace/stack_trace.dart';
+
+import 'live_test.dart';
+import 'state.dart';
+import 'suite.dart';
+import 'test.dart';
+
+/// An implementation of [LiveTest] that's controlled by a [LiveTestController].
+class _LiveTest extends LiveTest {
+  final LiveTestController _controller;
+
+  Suite get suite => _controller._suite;
+
+  Test get test => _controller._test;
+
+  State get state => _controller._state;
+
+  Stream<State> get onStateChange =>
+      _controller._onStateChangeController.stream;
+
+  List<AsyncError> get errors => new UnmodifiableListView(_controller._errors);
+
+  Stream<AsyncError> get onError => _controller._onErrorController.stream;
+
+  Future get onComplete => _controller.completer.future;
+
+  Future run() => _controller._run();
+
+  _LiveTest(this._controller);
+}
+
+/// A controller that drives a [LiveTest].
+///
+/// This is a utility class to make it easier for implementors of [Test] to
+/// create the [LiveTest] returned by [Test.load]. The [LiveTest] is accessible
+/// through [LiveTestController.liveTest].
+///
+/// This automatically handles some of [LiveTest]'s guarantees, but for the most
+/// part it's the caller's responsibility to make sure everything gets
+/// dispatched in the correct order.
+class LiveTestController {
+  /// The [LiveTest] controlled by [this].
+  LiveTest get liveTest => _liveTest;
+  LiveTest _liveTest;
+
+  /// The test suite that's running [this].
+  final Suite _suite;
+
+  /// The test that's being run.
+  final Test _test;
+
+  /// The function that will actually start the test running.
+  final Function _onRun;
+
+  /// The list of errors caught by the test.
+  final _errors = new List<AsyncError>();
+
+  /// The current state of the test.
+  var _state = const State(Status.pending, Result.success);
+
+  /// The controller for [LiveTest.onStateChange].
+  final _onStateChangeController = new StreamController<State>.broadcast();
+
+  /// The controller for [LiveTest.onError].
+  final _onErrorController = new StreamController<AsyncError>.broadcast();
+
+  /// The completer for [LiveTest.onComplete];
+  final completer = new Completer();
+
+  /// Whether [run] has been called.
+  var _runCalled = false;
+
+  /// Creates a new controller for a [LiveTest].
+  ///
+  /// [test] is the test being run; [suite] is the suite that contains it.
+  ///
+  /// [onRun] is a function that will be called from [LiveTest.run]. It should
+  /// start the test running. The controller takes care of ensuring that
+  /// [LiveTest.run] isn't called more than once and that [LiveTest.onComplete]
+  /// is returned.
+  LiveTestController(this._suite, this._test, void onRun())
+      : _onRun = onRun {
+    _liveTest = new _LiveTest(this);
+  }
+
+  /// Adds an error to the [LiveTest].
+  ///
+  /// This both adds the error to [LiveTest.errors] and emits it via
+  /// [LiveTest.onError]. [stackTrace] is automatically converted into a [Chain]
+  /// if it's not one already.
+  void addError(error, StackTrace stackTrace) {
+    var asyncError = new AsyncError(error, new Chain.forTrace(stackTrace));
+    _errors.add(asyncError);
+    _onErrorController.add(asyncError);
+  }
+
+  /// Sets the current state of the [LiveTest] to [newState].
+  ///
+  /// If [newState] is different than the old state, this both sets
+  /// [LiveTest.state] and emits the new state via [LiveTest.onStateChanged]. If
+  /// it's not different, this does nothing.
+  void setState(State newState) {
+    if (_state == newState) return;
+    _state = newState;
+    _onStateChangeController.add(newState);
+  }
+
+  /// A wrapper for [_onRun] that ensures that it follows the guarantees for
+  /// [LiveTest.run].
+  Future _run() {
+    if (_runCalled) {
+      throw new StateError("LiveTest.run() may not be called more than once.");
+    }
+    _runCalled = true;
+
+    _onRun();
+    return liveTest.onComplete;
+  }
+}