Comment by n144q
You are not supposed to spend a significant amount of time testing "behavior". Unit tests should be the vast majority of testing.
And I can tell you I have first hand experience of an "MVP" product getting delayed, multiple times, because management realizes that nobody wants to purchase our product when they discover how buggy and unusable it is.
We probably work on different kinds of projects and/or different kinds of teams? I'd rather have the majority being end-to-end/UI tests than unit tests most of the time because you're not going to know if your app or UI is broken otherwise. I tend to work in smaller teams where everyone is experienced, and use languages with decent type checking.
It's very possible to write great software without any tests at all too. It's like people forget that coders used to write assembly code without source control, CI, mocking and all that other stuff.