Most developers I talk to have this vague understanding about testing — they know they should do it, but they’re not always clear on which tests do what and why it matters. So you write a unit test here, run some manual clicks there, and hope the whole thing works. That’s not a strategy. Testing has distinct types for distinct purposes.
Let me walk you through what each testing type actually does and, more importantly, which ones companies genuinely implement versus which ones are nice-to-have theory.