How to setup yeoman test for subgenerator that reads package.json

I have a subgenerator that uses the name from the package.json. Now I want to test that function and wrote a before() that is supposed to create a dummy package.json for the test.

Problem is that the subgenerator cannot read the dummy json file.

test file:

before(function (done) {

  helpers.run(path.join( __dirname, '../addcomponent'))
  .inDir(path.join( __dirname, './tmp'), function(dir) {

    fs.copyTpl(
      path.join(__dirname, '../app/templates/_package.json'),
      dir + 'package.json',
      { ProjectName: 'foo' }
    );

    var test = fs.readJSON(dir + 'package.json');
    console.log('test: ' + test); // returns the object
    console.log('test.name: ' + test.name); // returns the correct name

  })
  .withArguments(['foo'])
  .withPrompts(prompts)
  .withOptions(options)
  .on('end', done);

});

but in my sub-generator:

var memFs = require('mem-fs');
var editor = require('mem-fs-editor');
var store = memFs.create();
var fs = editor.create(store);

...

init: function() {
  this.pkg = this.fs.readJSON('package.json');
  console.log('this.pkg: ' + this.pkg); // returns undefined
}
// or
init: function() {
  this.on('ready', function() {
    this.pkg = this.fs.readJSON('package.json');
    console.log('this.pkg: ' + this.pkg); // returns undefined
  });
}
// or
anyOther: function() {
  this.pkg = this.fs.readJSON('package.json');
  console.log('this.pkg: ' + this.pkg); // returns undefined
}

The whole setup can be found here: http://ift.tt/1JaLOcd

thanks for any help