In terms of business, you are trying to prove your business model. If your business model is bad, it doesn't matter how well your software is written. You need to prove your business model before you run out of funds.
It's a give and take. You really need to understand both the technical aspects and the business aspects to understand why entities might do certain things.
Also, people have been writing software without unit tests for decades.
Disagree - if your engineers don't write tests, you need to clearly state to them that tests are table stakes, and create an environment conducive to the outcome you want (set up CI, make it fast, set aside time for test-writing hackathons).
If your engineers don't want to _follow_ that leadership after it's given, then yeah, you hired the wrong people - but don't demonize employees for not doing something they weren't told they need to do.
Just telling engineers, "write tests" and then promoting the ones that don't is bad leadership: you need to create an environment where the behaviors you desire are the ones that are promoted.
How do you make sure that the refactored class does the same thing as the old one? Rewriting old code that you don't have test coverage for is way riskier than whatever small change you were going to make to it.
I write a lot of code without tests because a lot of legacy codebases aren't set up to be testable, but they work, and it's important to the business that we're able to deliver small bug fixes and incremental improvements on the existing code while we write whatever replacement system we want to write. As I work on them they'll slowly get more testable, but if you're abandoning working code because it has no tests, you're usually making the wrong decision. (Which the author recognizes.)
Solid integration tests may work, but it's hard to get really good coverage in any reasonable running time from integration tests.
These days I try to cover the happy path with a fairly integrated flavour of test, the edge cases around the tricky bits of code, and fairly exhaustive coverage for authentication / authorization code paths, and not a whole lot more.
If I wanted to be a consultant or contractor again, it would be walking into these situations and essentially building test systems for legacy code.
(And if anyone wants to pay me 8,000 a week for a few months...)
This. This is the problem. The answer, with tests.
Tests are simply the implementation of knowing what the code is expected to do. If you don't have any basis for that expectation, writing tests is meaningless - either you test the current behavior of the code, which doesn't help you change anything, or you test your imagined behavior of the code, which doesn't help you validate anything.
That's great if you have the luxury of time.
Good test coverage will definitely save you time in the long run, no doubt about it. But it will cost you dearly in the short term.
And if your company's life or death hangs on getting a feature out a couple days sooner, then skipping tests is a perfectly valid thing to do.