As probably discussed earlier, generating dungeons is hard. Difficult, even. Infuriating, if you will. Not because of generation itself, per se, but making it actually cohesive. If you're going with a grid system, how do you make sure the rooms don't overlap each other? If you're going for a gungeon type system, how do you make it mesh properly? If you're doing something non standard... how?

For games like slay the spire, inscryption, and other similar rouge-likes where you have a map without really connecting rooms, it's actually easy. But for more physical games like isaac, you need to make sure the rooms can't overlap each other and make it so you can't accidentally generate rooms on top of each other, or have rooms where they're not supposed to be.  Say a room without a door generates next to one with a door - what then?

Case in point, the hardest part is edge cases. There are many ways to circumvent them, but the fact remains that you still need to cover them, and not all of them can be covered with a simple, large test.