[n144q]

You (or other people) will thank yourself in a few months/years when refactoring the code, knowing that they don't need to worry about missing edge cases, because all known edge cases are covered with these non regression tests.

[seanwilson]

There's really no situation you wouldn't write a test? Have you not had situations where writing the test would take a lot of effort vs the risk/impact of the bug it's checking for? Your test suite isn't going to be exhaustive anyway so there's always a balance of weighing up what's worth testing. Going overkill with tests can actually get in the way of refactoring as well when a change to the UI or API isn't done because it would require updating too many tests.

[n144q]

I have, and in 90% of cases that's because my code is seriously messed up, so that (1) it is not easy to write a unit test (2) there has not been enough effort in testing so that mocks are not available when I need it.

Adding tests is not easy, and you can always find excuses to not do that and instead "promise" to do it later, which almost never happens. I have seen enough to know this. Which is why I myself have put more work in writing unit tests, refactoring code and creating test mocks than anyone else in my team.

And I can't tell you how much I appreciate it when I find that this has benefitted me personally -- when I need to write a new test, often I find that I can reuse 80% if not 80% of the test setup and focus on the test body.

After adding the first test, it becomes much easier to add the second and third test. If you don't add the first test or put the effort into making your code actually testable, it's never going to be easy to test anything.

[seanwilson]

I'm assuming here the code is written in a testable way, but the behaviour is hard or time-consuming to test.

It's not about being lazy or making excuses, it's not free to write exhaustive tests and the resources have to come from somewhere. For MVPs, getting the first release out is going to be much more important for example.

[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.

[seanwilson]

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.