MVP occurs a lot on Hacker News, in that context meaning Minimum Viable Product, or the least amount of work you must do to make it useful for users/customers.

BDD in the software context means Behaviour-Driven Design and is an opinionated way of writing tests.

With regards to step 3 in your example: Sometimes it can be challenging to design automated tests for certain functionality.

For a game, it could be scripting "fake" user input that is supposed to have a certain end result, and then verify that that end result actually occurred. E.g., the player makes a few good moves, then a few bad moves that should cause health to drop below 0, then check that the player actually died.

Automated tests are a life saver, and often it pays off in the end to learn how to write them for almost any functional requirement.

I hope I answered your questions!