Support parsing empty stack chains.

test/chain_test.dart

 // Copyright (c) 2013, 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 chain_test;
 
 import 'dart:async';
 
 import 'package:path/path.dart' as p;
 import 'package:stack_trace/stack_trace.dart';
@@ skipping 454 matching lines @@
         trace = stackTrace;
         return new Chain.forTrace(stackTrace);
       }
     });
 
     expect(chain.traces, hasLength(1));
     expect(chain.traces.first.toString(),
         equals(new Trace.from(trace).toString()));
   });
 
-  test('Chain.parse() parses a real Chain', () {
-    return captureFuture(() => inMicrotask(() => throw 'error')).then((chain) {
-      expect(new Chain.parse(chain.toString()).toString(),
-          equals(chain.toString()));
+  group('Chain.parse()', () {
+    test('parses a real Chain', () {
+      return captureFuture(() => inMicrotask(() => throw 'error'))
+          .then((chain) {
+        expect(new Chain.parse(chain.toString()).toString(),
+            equals(chain.toString()));
+      });
+    });
+
+    test('parses an empty string', () {
+      var chain = new Chain.parse('');
+      expect(chain.traces, isEmpty);
+    });
+
+    test('parses a chain containing empty traces', () {
+      var chain = new Chain.parse(
+          '===== asynchronous gap ===========================\n'
+          '===== asynchronous gap ===========================\n');
+      expect(chain.traces, hasLength(3));
+      expect(chain.traces[0].frames, isEmpty);
+      expect(chain.traces[1].frames, isEmpty);
+      expect(chain.traces[2].frames, isEmpty);
     });
   });
 
   test("toString() ensures that all traces are aligned", () {
     var chain = new Chain([
       new Trace.parse('short 10:11  Foo.bar\n'),
       new Trace.parse('loooooooooooong 10:11  Zop.zoop')
     ]);
 
     expect(chain.toString(), equals(
@@ skipping 310 matching lines @@
 ///
 /// [callback] is expected to throw the string `"error"`.
 Future<Chain> captureFuture(callback()) {
   var completer = new Completer<Chain>();
   Chain.capture(callback, onError: (error, chain) {
     expect(error, equals('error'));
     completer.complete(chain);
   });
   return completer.future;
 }