If you don't reason properly, no amount of testing will save you. It is only part (an important one, surely) of what you need to create reliable software.
I saw too many developers in a cycle like this:
test->bang keyboard->test again (not working)->bang keyboard (now a hack) ->test again(still not working - let's try one more thing)->bang keyboard->test again (it works - Don't touch it!)
which is why early focus on testing doesn't seem very sound advice. The original post is about "Career Advice For Young Developers" - and for a young developer, focusing on careful thinking is better than focusing on testing.
I saw too many developers in a cycle like this:
test->bang keyboard->test again (not working)->bang keyboard (now a hack) ->test again(still not working - let's try one more thing)->bang keyboard->test again (it works - Don't touch it!)
which is why early focus on testing doesn't seem very sound advice. The original post is about "Career Advice For Young Developers" - and for a young developer, focusing on careful thinking is better than focusing on testing.