I applied through a recruiter who passed my CV over to IG. I got a phone interview and this had some JavaScript questions. I didn't know all of the answers but that went okay. They got back to me the same day and invited me to an assessment centre. The assessment day consisted of four tasks. First was a technical test, this was ~20 questions on Java (a mistake was made by someone as I should have received a JavaScript test). The next task was a pair programming session with a developer. I sat with a JavaScript developer and worked through some issues (this was quite basic; more of an interview/skill-tester but you sat at a computer). The third was a numerical exercise which was split into two tasks: a basic maths exercise where you have 5 minutes to answer as many addition, subtraction, multiplication and division questions as possible out of 100 questions and an SHL paper. Finally, there was a group task which was more relaxed - we had to come up with a game out of various pieces of equipment they found around the office (paper plates, paper clips etc.) and then pitch it to the assessors. The final stage (which I didn't reach) would have been a competency-based interview with a member of HR.