They're not "making an API testing client". They're trying to start something called a "business". People do this to try to get enough of this thing called "money", to pay for the costs in their lives and their family's lives.

If they are based in America, they would be calculating at least, say $200k per year per employee, since they need to pay healthcare etc. So multiply that by the number of employees you want in your business, then add all the other costs, and extend over the period you want the funding to cover.