I work for asda, my 'asda magic' (the name of it really makes me cringe lol) interview we did a roll play, we were divided into groups and were given an asda product and we had to act out an advert for it, tbh i found it really embarrassing but I always hated performing in front of others. We also had a tour around the store and were paired up and asked each other questions and then had to share what the other person had told us about themselves, again I found this embaressing as I hate any kind of public speaking, then we had an interview with one of the people there. Oh and we also watched a few videos whilst writing down the answers to questions relating to the videos on a work sheet.
I think it varies from store to store because I had a group interview with another store before this one and it was a bit different, instead of roll play we had to make a model out of spaghetti and blue tack, and the individual interviews were done on a different day and we watched the videos without having to follow a sheet.
I don't think they offer anything extra maternity pay wise, it's just the standard smp providing you work enough hours per week. They're ok to work for but I'm not gonna lie I've had a few problems, it does vary on the store though.
Each store has to follow the same policy but some things are done differently at different stores. For example I do loads of overtime without being asked and apart from the first two weeks have never done a week where i'm working just my contact hours. However a friend at another store only ever seemed to work her contract and was always asked about extra shifts, they actually had a book where you write if you're available/want to do any extra shifts we don't have anything like that here.
Good luck! I hope I havn't put you off or anything, just giving you my experience. Just be yourself, smile lots and be as friendly as possible with everyone. It's not the worst place to work but imo isn't the best either. What department have you applied for?