Your resume, what you say in the interview, even the above test task the manager learns all this from your mouth. Is it true what you say or write? And will you be just as good when you are hired, as in an interview or test assignments? These are all risk factors, and no one likes to risk. There is a simple way to dispel manager’s doubts to show an example of your activity from the everyday, real world. Post your CVs to your resume on professional social networks such as LinkedIn, societies like dev.by or Habrahabr. If you have open source projects go ahead, show that you can write good code not in words but in deeds! We should also say about StackOverflow.