As in previous years, there were still a few days between back-to-school day and the official start of term. Fred and George spent those days conducting market research at Hogwarts.
Although they were in their seventh year, which meant they had no end-of-year exams, they did have the much more demanding Nastily Exhausting Wizarding Test. Yet clearly, neither of them cared about that thing in the slightest.
Their potions and joke products business earned several times more in a year than Mr. Weasley, the second-in-command of a small department at the Ministry of Magic, had earned in decades. Under those circumstances, what did the twins need Nastily Exhausting Wizarding Test certificates for?
The main purpose of a Nastily Exhausting Wizarding Test certificate was to get a foot in the door when looking for work, much like a diploma in the Muggle world.
But would the twins need to look for jobs? Would they need to work for someone else?
If you asked the two of them, they would tell you with absolute conviction, "Work for someone else? Not a chance. Not in this lifetime."
With no exams to worry about, and this being their final year at school, the twins could naturally enjoy themselves as much as they liked. Besides, to keep their ideas from losing touch with young wizards' actual needs after graduation, they were also recruiting contacts at school.
They did not ask the young wizards to do anything beyond telling them about the bizarre things they wanted to make. Put plainly, they wanted ideas. The twins would not only bring those ideas to life but also give them a set for free.
In the Muggle world, this would have been blatant plagiarism of other people's ideas, but there was no such notion in the wizard world. The