anchor.diff:  
         expect(chain.terse.toString(), equals(
             'dart:core             Bar.baz\n'
  -          'user/code.dart 10:11  Bang.qux\n'
  +          '$userSlashCode 10:11  Bang.qux\n'
             'dart:core             Zop.zoop\n'
             '===== asynchronous gap ===========================\n'
  -          'user/code.dart 10:11  Bang.qux\n'
  +          '$userSlashCode 10:11  Bang.qux\n'
             'dart:core             Zip.zap\n'
  -          'user/code.dart 10:11  Zop.zoop\n'));
  +          '$userSlashCode 10:11  Zop.zoop\n'));
       });
   
       test('eliminates internal-only traces', () {
  
positive.code:     });
    });
  
    group('Chain.terse', () {
      test('makes each trace terse', () {
        var chain = new Chain([
  
negative.code:     ]).toTrace();
  
      expect(trace.toString(), equals(
          '$userSlashCode 10:11  Foo.bar\n'
          'dart:core 10:11       Bar.baz\n'
          '$userSlashCode 10:11  Foo.bar\n'
          'dart:core 10:11       Bar.baz\n'));
    });
  
  