This won't work if the exclude option is an array of files to exclude, which in many cases it will be. This will need to be modified to be more similar to

    options.exclude.indexOf(file.path)

But that won't exactly work since ```file.path``` is an absolute path now - the exclusions should all be relative. Perhaps we can use: 

     if (options.exclude) {
      if (options.exclude.indexOf(file.relative) >= 0) {
        return;
      } 
    }

I modified your test cases by setting ```exclude: ['file2.js', 'file4.js']```, creating that ```file4.js```, asserting that it was excluded and everything passed well after that. Is there anything else that needs to be done?