Rakuten uses Codility to test candidates. After applying for the job, a link to the test was sent to me. The test could be taken anytime within a week, and I had a hour to solve the problem once the test starts. There were various languages that can be chosen from. (C was not included) I think it’s better to get familiar with the online test platform prior to the test, because you only get a hour. And I think posts reviewing helps. It seems to have a set of problems that Rakuten has been using for years. For example, rectilinear rectangles problem is mentioned multiple times in the posts. The problem I had was not rectilinear rectangles problem, but was also mentioned in one of the posts.