You need both automated and manual testing for a high-quality product. However, this level of quality is not strictly necessary for most products or projects, and so you see most shops today preferring the cheaper alternative.
Automated testing is perhaps an order of magnitude cheaper. Written once, run thousands of times, protecting the project, potentially for decades. The sooner you find the bug, less people need to be involved to fix it. Including customers that might turn away. (That's why the renewed interest in typing and linters that find bugs before you even finish writing a statement.)
The reason automated testing is necessary is that humans get bored quickly. They are needed to prevent subtle (and not so) regressions not obvious at a glance.
Humans are a lot more clever though, so can provide insight on a higher level, though at higher cost. That cost may be worth paying. If your product is mission critical or adjacent, and the customer is willing to pay for that "insurance."
You need both automated and manual testing for a high-quality product. However, this level of quality is not strictly necessary for most products or projects, and so you see most shops today preferring the cheaper alternative.
Automated testing is perhaps an order of magnitude cheaper. Written once, run thousands of times, protecting the project, potentially for decades. The sooner you find the bug, less people need to be involved to fix it. Including customers that might turn away. (That's why the renewed interest in typing and linters that find bugs before you even finish writing a statement.)
The reason automated testing is necessary is that humans get bored quickly. They are needed to prevent subtle (and not so) regressions not obvious at a glance.
Humans are a lot more clever though, so can provide insight on a higher level, though at higher cost. That cost may be worth paying. If your product is mission critical or adjacent, and the customer is willing to pay for that "insurance."