But 20 years ago is now 2006, and unit tests were well established as a best practice.I agree with the spirit of what you wrote, but my recollection of the timeline is different. The first decade of the 2000s was peak Crazy Agile Advocacy, but IIRC it wasn’t until the 2010s that unit testing really became almost universal practice. Much before that and it was still tangled up with XP, TDD and lots of other things that certainly weren’t universally accepted as good practices (notwithstanding the strident advocacy of a certain group of consultants/authors/speakers/bloggers and their fans).
I remember, back in the mid-2000s, when we had some consultants brought in to talk about different aspects of quality and testing. There were several working groups, each led by one of those external consultants, and one of them was about unit testing. This was in a relatively large software development organisation for the time, a few thousand people, and while some parts of the organisation had some form of automated testing operating by then, it definitely was not the case that the well-known products produced by the organisation all had a unit test suite. Other practices we’d consider routine today, such as peer code reviews, were also in their infancy during that period: some were doing them, many were not, and generally we had much less experience of how to do them effectively than we have today.
As an industry, I don’t think we really matured in how even the most ardent fans of unit testing were writing test suites until the 2010s either. In the 2000s, we still had lots of people mocking the entire universe and then writing unit tests that were 99% testing those mocks because of 100% test coverage requirements, and similar dogmatic nonsense.
By the 2020s, I think there was much more awareness of that automated testing is generally a good idea, but there are different kinds/levels of automated testing and finding a mix that suits each project’s specific needs is important. One of the great benefits from the more recent AI tools, particularly the agentic ones over the past year or so, has been that it has clearly demonstrated both the value of a good automated test strategy and how much of a waste of time vacuous tests are.