Spotify wrote a brilliant blog post on this. Highly recommend reading.

https://labs.spotify.com/2014/02/28/how-to-shuffle-songs/

I have a theory that Spotify doesn't do random shuffling, but weighted shuffling, so that new items are more likely to be at the top of a shuffle (or maybe even popular items). I also believe that this will satisfy users better than true random shuffling.

About your linked post: You don't test the randomness of the shuffling, you only test if a shuffled list contain one and only of each original item.

Spotify's shuffling is most certainly not random. Every once in a while I get a bug where it simply shuffles through various songs from 4-5 albums and will never pick songs outside that set. Restarting the app corrects the behaviour. To me that's some level of proof, because the songs are all there. So what's the algorithm really doing?

I appreciate the simplicity of your site but it is definitely difficult to quickly see where one post ends and another one starts.

On your website you put a source mark on the statement 'This is the same reason the Brits mistakenly assumed that the Germans had an exceptionally good aim with their V-1 flying bombs during World War II '

I'd like to read about this, do you still have the intended link?