I just did this and it works flawlessly. Follow this link http://expertzone.microsoft.com/Home.aspx
and register. Go to the "Xbox One Assessment". Don't bother looking over the review materials, you have four tries to get 80%. I took it twice, first time got 65%, next try got 85% (questions do change a bit). You must work in retail and provide a copy of your Pay Stub before you can take the test. Once you take it, you'll get the promo code on the page of the test.
Questions? YMMV depending on the store you work at.
Second note: Microsoft is only giving out 30,000 of these. Not sure how many have already been given out but it's been running since 10/7/13. Again, YMMV.
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