Don't wrap exceptions in complete or completes().

lib/src/frontend/future_matchers.dart

 // Copyright (c) 2012, 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 test.frontend.future_matchers;
 
 import 'dart:async';
 
 import 'package:matcher/matcher.dart' hide throws, throwsA, expect, fail;
 
 import '../backend/invoker.dart';
 import '../utils.dart';
 import 'expect.dart';
 
 /// Matches a [Future] that completes successfully with a value.
 ///
 /// Note that this creates an asynchronous expectation. The call to `expect()`
 /// that includes this will return immediately and execution will continue.
 /// Later, when the future completes, the actual expectation will run.
 ///
 /// To test that a Future completes with an exception, you can use [throws] and
 /// [throwsA].
-final Matcher completes = const _Completes(null, '');
+final Matcher completes = const _Completes(null);
 
 /// Matches a [Future] that completes succesfully with a value that matches
 /// [matcher].
 ///
 /// Note that this creates an asynchronous expectation. The call to
 /// `expect()` that includes this will return immediately and execution will
 /// continue. Later, when the future completes, the actual expectation will run.
 ///
 /// To test that a Future completes with an exception, you can use [throws] and
 /// [throwsA].
 ///
-/// [description] is an optional tag that can be used to identify the completion
-/// matcher in error messages.
-Matcher completion(matcher, [String description = '']) =>
-    new _Completes(wrapMatcher(matcher), description);
+/// The [description] parameter is deprecated and shouldn't be used.
+Matcher completion(matcher, [@deprecated String description]) =>
+    new _Completes(wrapMatcher(matcher));
 
 class _Completes extends Matcher {
   final Matcher _matcher;
-  final String _id;
 
-  const _Completes(this._matcher, this._id);
+  const _Completes(this._matcher);
 
   bool matches(item, Map matchState) {
     if (item is! Future) return false;
     Invoker.current.addOutstandingCallback();
 
     item.then((value) {
       if (_matcher != null) expect(value, _matcher);
       Invoker.current.removeOutstandingCallback();
-    }, onError: (error, trace) {
-      if (error is TestFailure) throw error;
-
-      var id = _id == '' ? '' : '${_id} ';
-      var reason = 'Expected future ${id}to complete successfully, '
-          'but it failed with ${error}';
-      if (trace != null) {
-        var stackTrace = terseChain(trace,
-            verbose: Invoker.current.metadata.verboseTrace);
-        stackTrace = '  ${stackTrace.toString().replaceAll('\n', '\n  ')}';
-        reason = '$reason\nStack trace:\n$stackTrace';
-      }
-      fail(reason);
     });
 
     return true;
   }
 
   Description describe(Description description) {
     if (_matcher == null) {
       description.add('completes successfully');
     } else {
       description.add('completes to a value that ').addDescriptionOf(_matcher);
     }
     return description;
   }
 }