anchor.diff:  bool formatStacks = true;
   
   /// A flag that controls whether we try to filter out irrelevant frames from
  -/// the stack trace. Requires formatStacks to be set.
  +/// the stack trace.
  +///
  +/// Requires [formatStacks] to be set.
   bool filterStacks = true;
   
   void _requireNotRunning() {
  
positive.code: }
  
  /// Indicate that [callback] is expected to be called a [count] number of times
  /// (by default 1). The unittest framework will wait for the callback to run the
  /// specified [count] times before it continues with the following test.  Using
  /// [expectAsync] will also ensure that errors that occur within [callback] are
  /// tracked and reported. [callback] should take 0 positional arguments (named
  /// arguments are not supported). [id] can be used to provide more
  /// descriptive error messages if the callback is called more often than
  /// expected. [max] can be used to specify an upper bound on the number of
  /// calls; if this is exceeded the test will fail (or be marked as in error if
  /// it was already complete). A value of 0 for [max] (the default) will set
  /// the upper bound to the same value as [count]; i.e. the callback should be
  
negative.code: 
  Configuration _config;
  
  /// [Configuration] used by the unittest library.
  ///
  /// Note that if a configuration has not been set, calling this getter will
  /// create a default configuration.
  Configuration get unittestConfiguration {
    if (_config == null) {
      _config = new Configuration();
  