Add an Invoker class that manages a running test.

lib/src/invoker.dart

Index: lib/src/invoker.dart
diff --git a/lib/src/invoker.dart b/lib/src/invoker.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.invoker;
+
+import 'dart:async';
+
+import 'package:stack_trace/stack_trace.dart';
+
+import 'expect.dart';
+import 'live_test.dart';
+import 'live_test_controller.dart';
+import 'state.dart';
+import 'suite.dart';
+import 'test.dart';
+import 'utils.dart';
+
+/// A test in this isolate.
+class LocalTest implements Test {
+  /// The name of the test.
+  final String name;
+
+  /// The test body.
+  final AsyncFunction _body;
+
+  /// The callback used to clean up after the test.
+  ///
+  /// This is separated out from [_body] because it needs to run once the test's
+  /// asynchronous computation has finished, even if that's different from the
+  /// completion of the main body of the test.
+  final AsyncFunction _tearDown;
+
+  LocalTest(this.name, body(), {tearDown()})
+      : _body = body,
+        _tearDown = tearDown;
+
+  /// Loads a single runnable instance of this test.
+  LiveTest load(Suite suite) {
+    var invoker = new Invoker._(suite, this);
+    return invoker.liveTest;
+  }
+}
+
+/// The class responsible for managing the lifecycle of a single local test.
+///
+/// The current invoker is accessible within the zone scope of the running test
+/// using [Invoker.current]. It's used to track asynchronous callbacks and
+/// report asynchronous errors.
+class Invoker {
+  /// The live test being driven by the invoker.
+  ///
+  /// This provides a view into the state of the test being executed.
+  LiveTest get liveTest => _controller.liveTest;
+  LiveTestController _controller;
+
+  /// The test being run.
+  LocalTest get _test => liveTest.test as LocalTest;
+
+  /// Note that this is meaningless once [_onCompleteCompleter] is complete.
+  var _outstandingCallbacks = 0;
+
+  /// The completer to complete once the test body finishes.
+  ///
+  /// This is distinct from [_controller.completer] because a tear-down may need
+  /// to run before the test is truly finished.
+  final _completer = new Completer();
+
+  /// The current invoker, or `null` if none is defined.
+  ///
+  /// An invoker is only set within the zone scope of a running test.
+  static Invoker get current => Zone.current[#unittest._invoker];
+
+  Invoker._(Suite suite, LocalTest test) {
+    _controller = new LiveTestController(suite, test, _onRun);
+  }
+
+  /// Tells the invoker that there's a callback running that it should wait for
+  /// before considering the test successful.
+  ///
+  /// Each call to [addOutstandingCallback] should be followed by a call to
+  /// [removeOutstandingCallback] once the callbak is no longer running. Note
+  /// that only successful tests wait for outstanding callbacks; as soon as a
+  /// test experiences an error, any further calls to [addOutstandingCallback]
+  /// or [removeOutstandingCallback] will do nothing.
+  void addOutstandingCallback() {
+    _outstandingCallbacks++;
+  }
+
+  /// Tells the invoker that a callback declared with [addOutstandingCallback]
+  /// is no longer running.
+  void removeOutstandingCallback() {
+    _outstandingCallbacks--;
+
+    if (_outstandingCallbacks != 0) return;
+    if (_completer.isCompleted) return;
+
+    // The test must be passing if we get here, because if there were an error
+    // the completer would already be completed.
+    assert(liveTest.state.result == Result.success);
+    _completer.complete();
+  }
+
+  /// Notifies the invoker of an asynchronous error.
+  ///
+  /// Note that calling this explicitly is rarely necessary, since any
+  /// otherwise-uncaught errors will be forwarded to the invoker anyway.
+  void handleError(error, [StackTrace stackTrace]) {
+    if (stackTrace == null) stackTrace = new Chain.current();
+
+    var afterSuccess = liveTest.isComplete &&
+        liveTest.state.result == Result.success;
+
+    if (error is! TestFailure) {
+      _controller.setState(const State(Status.complete, Result.error));
+    } else if (liveTest.state.result != Result.error) {
+      _controller.setState(const State(Status.complete, Result.failure));
+    }
+
+    _controller.addError(error, stackTrace);
+
+    if (!_completer.isCompleted) _completer.complete();
+
+    // If a test was marked as success but then had an error, that indicates
+    // that it was poorly-written and could be flaky.
+    if (!afterSuccess) return;
+    handleError(
+        "This test failed after it had already completed. Make sure to use "
+            "[expectAsync]\n"
+        "or the [completes] matcher when testing async code.",
+        stackTrace);
+  }
+
+  /// The method that's run when the test is started.
+  void _onRun() {
+    _controller.setState(const State(Status.running, Result.success));
+
+    Chain.capture(() {
+      runZoned(() {
+        // TODO(nweiz): Make the timeout configurable.
+        // TODO(nweiz): Reset this timer whenever the user's code interacts with
+        // the library.
+        var timer = new Timer(new Duration(seconds: 30), () {
+          if (liveTest.isComplete) return;
+          handleError(
+              new TimeoutException(
+                  "Test timed out after 30 seconds.",
+                  new Duration(seconds: 30)));
+        });
+
+        addOutstandingCallback();
+
+        // Run the test asynchronously so that the "running" state change has a
+        // chance to hit its event handler(s) before the test produces an error.
+        // If an error is emitted before the first state change is handled, we
+        // can end up with [onError] callbacks firing before the corresponding
+        // [onStateChange], which violates the timing guarantees.
+        new Future(_test._body)
+            .then((_) => removeOutstandingCallback());
+
+        // Explicitly handle an error here so that we can return the [Future].
+        // If a [Future] returned from an error zone would throw an error
+        // through the zone boundary, it instead never completes, and we want to
+        // avoid that.
+        _completer.future.then((_) {
+          if (_test._tearDown == null) return null;
+          return new Future.sync(_test._tearDown);
+        }).catchError(Zone.current.handleUncaughtError).then((_) {
+          timer.cancel();
+          _controller.setState(
+              new State(Status.complete, liveTest.state.result));
+          _controller.completer.complete();
+        });
+      }, zoneValues: {#unittest._invoker: this}, onError: handleError);
+    });
+  }
+}