"The recent test."
Translation:Το πρόσφατο τεστ.
Not every test is an exam. Διαγώνισμα only describes a written school exam, as Yiannis49 explains in his comment. Then you have tests/τεστ that may be for academic or diagnostic purposes for example. The sentence here does not provide any context one way or another so if you use διαγώνισμα you are narrowing down the context in your translation.
I suggest looking up the pages for the 'related' words both in EN and in GR on a dictionary that offers usage examples, like wordreference. If you move from one page to another (διαγώνισμα - exam - τεστ) you will get a better idea about where the overlap is between the two languages.