Add RuntimeError to default expectations and handle expectation groups correctly.

pkg/testing/lib/src/expectation.dart

 // Copyright (c) 2017, 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.md file.
 
 library testing.expectation;
 
 /// An expectation represents the expected outcome of a test (or if it should
 /// be skipped).
 ///
 /// An expectation belongs to a group, for example, [ExpectationGroup.Fail].
@@ skipping 16 matching lines @@
 
   static const Expectation Skip =
       const Expectation("Skip", ExpectationGroup.Skip);
 
   final String name;
 
   final ExpectationGroup group;
 
   const Expectation(this.name, this.group);
 
+  /// Returns the canonical expectation representing [group]. That is, one of
+  /// the above expectations (except for `Meta` which returns `this`).
+  Expectation get canonical => fromGroup(group) ?? this;
+
   String toString() => name;
+
+  static Expectation fromGroup(ExpectationGroup group) {
+    switch (group) {
+      case ExpectationGroup.Crash:
+        return Expectation.Crash;
+      case ExpectationGroup.Fail:
+        return Expectation.Fail;
+      case ExpectationGroup.Meta:
+        return null;
+      case ExpectationGroup.Pass:
+        return Expectation.Pass;
+      case ExpectationGroup.Skip:
+        return Expectation.Skip;
+      case ExpectationGroup.Timeout:
+        return Expectation.Timeout;
+    }
+    throw "Unhandled group: '$group'.";
+  }
 }
 
 class ExpectationSet {
   static const ExpectationSet Default =
       const ExpectationSet(const <String, Expectation>{
     "pass": Expectation.Pass,
     "crash": Expectation.Crash,
     "timeout": Expectation.Timeout,
     "fail": Expectation.Fail,
     "skip": Expectation.Skip,
     "missingcompiletimeerror":
         const Expectation("MissingCompileTimeError", ExpectationGroup.Fail),
     "missingruntimeerror":
         const Expectation("MissingRuntimeError", ExpectationGroup.Fail),
+    "runtimeerror": const Expectation("RuntimeError", ExpectationGroup.Fail),
   });
 
   final Map<String, Expectation> internalMap;
 
   const ExpectationSet(this.internalMap);
 
   operator [](String name) {
     return internalMap[name.toLowerCase()] ??
         (throw "No expectation named: '$name'.");
   }
@@ skipping 55 matching lines @@
     case "Pass":
       return ExpectationGroup.Pass;
     case "Skip":
       return ExpectationGroup.Skip;
     case "Timeout":
       return ExpectationGroup.Timeout;
     default:
       throw "Unrecognized group: '$name'.";
   }
 }