Not a lot. You will learn how to do all sorts of random things.
You will be heaped with work, given no positive feedback, get pulled into things outside your remit. You will then be let go if you don't come up to their impossible standards, there is no chance for you to improve as the management team is too inexperienced to help. The atmosphere in most teams is poor.
Advice to Management
If you march people out of the building, because you have seen them do that in movies, it is a good idea to remember to to take their keys.
The process took 2+ months. I interviewed at Lesara (London, England) in October 2017.
1st & 2nd round were good - final with Roman was poor. Firstly, I wasn't offered a drink. Secondly we had to interview in a very dimly lit room. Thirdly (and most importantly for me) the #1 corporate value is "bold in content, modest in style" ... Then why does the CEO wear a Rolex to interviews? ;)
Overall I got a poor vibe from him (and to be honest think it might be funny to base a character on him for the show Silicon Valley.)