If someone who has just begun a new job has a baptism of fire, they immediately have to cope with many severe difficulties and obstacles.

e.g., It was Mark’s first introduction to royal duties, and he came through his baptism of fire unscathed.

In my first month, I was given a million-dollar project to manage—it was a real baptism of fire.

In the world of academia, the pursuit of tenure is a baptism of fire to prove one’s research significance and serves as a rite of passage marking a major milestone in one’s career.—Ellen Choi, Forbes, 28 Oct. 2024

Translation: batismo de fogo/ prova de fogo.