I would like to point out that it's usually a bad idea to ask to do something before knowing what it actually entails. For all we know to test you have to submit two different AC solutions that both have the same SHA256 sum.

I think testers' main job is to write some solutions that should fail and check them to fail. Coming up with some solutions like this isn't always an easy job.

As a tester its your job to public write its great problems and private explain the problemsetter how to write great problems.

How to become a tester?

Be invited by an author or coordinator. It is ultimately their decision, not yours. Many testers have some connection with the author or coordinator, whether it's by being a friend, or an author of a previous contest, etc.

What do testers do?

Get free contribution points.

Testers take the contest virtually before the problems are publicly available, and provide feedback to the round.

What good are testers?

As an author, testers help you make sure:

• there are no bugs in the preparation of the round (intended solution, validator, checker, interactor, etc.)
• the problem statements are easy to understand, and translated well
• the problem difficulties are balanced
• wrong solutions are likely to fail the samples and pretests
• the problems are not too boring/standard, appeared before, or should not be used for some other reason
• the score distribution is reasonable

BTW, your graph is continuously differentiable XD.