Testing isn't only the end-to-end level

And it isn't even ... at the unit-test level of your application. Testing doesn't stop there!

Today's complex systems, with all this artificial intelligence inside, are built on components that are no less complex. Those components may not need to be tested separately — they've already been tested. But they were tested by people, and people can make mistakes.

Of course, no senior engineer is going to know every one of those components in depth. But you do need to have a sense of them: how they might affect the outcome, the security, the performance.

(Image is generated by Gemini)