After sending my CV and Covering letter I was informed that I had to pass a maths test.
It was a Kenexa test, so make sure you practice some of them if you have access to them (my uni offered some Kenexa practice tests).
After passing the test I had a telephone interview with a very friendly HR employee. It was mostly a competency interview but at the end she asked me to give her a SWOT analysis of a L'Oreal product and also speak about a L'Oreal TV ad that I like.
The final stage was the Assessment Centre. It was from 9am until 5pm. During that time I had a group exercise, a presentation (based on a case study that they gave us) and an interview. The people were very friendly and they tried to make this experience as stress-less as possible. Also, the time was more than enough to prepare for all the exercises.