Would I be happy working for this person?
"I will only hire someone to work directly for me if I would work for that person," Zuckerberg told a group in Barcelona who participated in the Facebook co-founder's monthly town hall meeting. "It's a pretty good test."
One of those people who passed the test was clearly Facebook's Chief Operating Officer Sheryl Sandberg.
When asked by a woman in the audience what it is like to work with Sandberg, Zuckerberg said he considered her a mentor and someone who has been instrumental in building Facebook into a business and "healthy organization."
Zuckerberg was in Barcelona for the Mobile World Congress where he spoke about the strides his Internet.org initiative has made in the developing world since he first announced its launch on year ago.
More than 7 million people in developing countries have benefited so far from having Internet access from their phones, according to Zuckerberg. With 50 million people living in the countries that are covered by the app, that number is likely to increase.