Yes that stood out to me as well. I think HackerRank is more widely used, and a large number of employers use neither test.
It’s used by many companies for screening internship and new grads applicants. More on this below.
It definitely is not. What CodeSignal offers is a set of coding challenges to supposedly test candidates’ programming skills. The challenges are like programming puzzles and what the vast majority of successful candidates do, is prepare for such challenges via LeetCode or similar sites.
I am not a fan of using CodeSignal or HackerRank for these initial screens because it only tests for a particular type of ability, and in real life I’ve worked with excellent software engineers who would have done badly on these tests. But I can see why it’s helpful to companies (like the FAANGs) that receive far more applicants than they can manually screen.
So… I’m going to take this ranking list with a large grain of salt. It’s based on only one metric (and not a particularly good one IMO) and (no surprise) the ranking is produced by the company that’s trying to popularize their product.