On HN, it's not debatable: you should definitely do it. Everywhere I've ever worked, it's also not debatable: no time or effort should be "wasted" writing unit tests, that's what QA is for.
> no time or effort should be "wasted" writing unit tests, that's what QA is for.
This is not my experience at all, everywhere I worked unit tests are required.
I don't agree at all, writing unit tests is not a waste of time, this sentiment comes from people who don't know how to avoid brittle tests.
It's impossible for QA to test every single path in your code. Unless you wanna cover all of those in your slow end to end tests?
Oh, you're preaching to the choir here, pal. It's incredibly frustrating. I have reason to hope, though... when I first started programming in the 90's, I would fight with my co-workers about using version control (I insisted on it, they said it was a waste of time). Now, people who oppose version control are off selling life insurance or whatever happens to people who probably shouldn't be writing computer programs.
The utility of a unit test suite is roughly proportional to the amount of in-process computation you do. “Glue” systems which mostly transform from one protocol to another usually need more integration systems than unit, making skipping unit tests not disastrous.
On legacy code? Alas. The amount of changes you might have to make to make the legacy code unit testable versus the benefit of unit tests can be exceedingly significant.
For instance, if the implementation involves calling up a bunch of value objects from a database, each of which do the same, and all of the code is inhouse so there is no standard mock or stub libraries available, adding unit tests is tantamount to rewriting the whole system without tests.
Existing codebases can also be too complicated for a few people to formalise into unit tests. The algorithm itself might be simple, but again, to discover that, you need to rewrite the whole system without tests. (You can add tests, of course, but when you're adding tests, you're making an assertion you cannot prove. Since you don't know what the code is meant to do, you don't know whether the tests are complete or even accurate.)
Once you're coding in a world where tests passing or tests failing has almost no predictive value on success or failure in release, you're working in a self-fulfilling prophecy where the code will never be tested because the tests literally make things worse.
Many codebases clearly do not have any automated tests at all, but unit tests can be the hardest to add onto a system after the fact.
Unit tests are code, and all code has a cost. Writing unit tests without any benefit is harmful behaviour.
Real world example: testing dumb getters/setters.
If you live in OOP land and have a natural aversion to directly accessing the data then by all means, write all the getters and setters you want.
But testing that "int getX() { return X;}" actually returns X is pathological behaviour. It's harmful because 1) it costs to write 2) it costs to read 3) it takes up space, distracting from more important tests 4) it costs to run 5) prevents you from easily making changes (it's a brittle test). Can't really see any benefits; if you manage to screw up writing a dumb getter, how do you trust yourself that the test code isn't wrong as well?
Yes. For a lot of smaller (web) applications where it is obvious if it isn't working correctly it just become a time sink. Everything in engineering is a set of trade-offs.
With regards to TDD specifically. It isn't for everyone and many consider it to be a bit of a cult. While I don't consider it a cult, It doesn't work with how I personally solve problems. I normally for example get something extremely rough working and then iterate until I consider it to be perfect and then write my tests to define how it should behave.
Oh, yes. We've still got a bunch of Real Programmers [1] out there. Real Programmers have moved on in my lifetime from insisting that everything should be written in assembly to insisting that they're Real Programmers enough to handle C directly and anyone who writes undefined behavior or buffer overflows or memory management issues just aren't Real Programmers enough and should put down their keyboards and walk away in shame, perhaps taking up goat farming or plumbing.
In all seriousness, their numbers seem to be diminishing. But you certainly can't expect the Real Programmers to write test code. Why should a programmer write test code when they know they didn't write any bugs?