code: function (ppunit, writer) {
      Dependencies.super_.call(this, ppunit, writer)
      var self = this
  
      self.subGraphs = []
  
      ppunit.on('start', function () {
          writer.write('digraph PPUnit {')
          self.printNodes()
          self.printSubGraphs()
          self.printDependencies()
          writer.write('}')
      })
  }
docs: Outputs graphviz dot notation of the test dependency graph
  
  @param {PPUnit} ppunit PPUnit instance
  @param {Object} writer An object that has a write method
  @param {function} writer.write A method that writes the output
  
  @constructor