What does it mean to "keep" the software? You can return the installation media, and say you erased the program, without having erased it.
I would say that if you work for Microsoft and they give you a program free in order to test, then it's not a form of income. The program doesn't represent monetary value in that situation. Microsoft, the copyright holder, is licensing you to have a copy of that program under terms which do not involve exchange of money.
This interpretation could be strengthened if the medium were marked as not for sale or resale.
Something given to you cannot count as income if you cannot resell it, or not legally.
The interpretation could be further strengthened if the gifted software is not entitled to any support.
Now let's think about dual licensing. Suppose you can obtain a proprietary version of a program for $100, or you can get it free under a copyleft license. It's exactly the same program, just packaged with different licenses. Have you received $100 worth of income? Or is it nothing, because the free one comes with no support?
I would say that if you work for Microsoft and they give you a program free in order to test, then it's not a form of income. The program doesn't represent monetary value in that situation. Microsoft, the copyright holder, is licensing you to have a copy of that program under terms which do not involve exchange of money.
This interpretation could be strengthened if the medium were marked as not for sale or resale.
Something given to you cannot count as income if you cannot resell it, or not legally.
The interpretation could be further strengthened if the gifted software is not entitled to any support.
Now let's think about dual licensing. Suppose you can obtain a proprietary version of a program for $100, or you can get it free under a copyleft license. It's exactly the same program, just packaged with different licenses. Have you received $100 worth of income? Or is it nothing, because the free one comes with no support?