No - there is no general requirement to be fair to all applicants when selecting someone for a job. It's not even clear how this would work - you would need to define what "fair" means in this context, and there would be many competing definitions. Is it fair to prefer an applicant who has more experience because they received help from their parents with landing their first job? Is it fair to prefer someone with a certain look for an acting job?
Is it fair to prefer someone who happens to have a similar personality to the person hiring?
So if the employer finds it more convenient to use the same test every year, and if they do not mind that this gives some applicants an advantage, they are free to do that.
The only exception is that discrimination based on certain, specific factors (often called "protected characteristics") is usually outlawed. The list depends on jurisdictions, but usually includes things like gender, race and age. However, even in that case discrimination is allowed if the business can demonstrate a genuine need - for example, when looking for an actor, it is allowed to hire based on gender.