the tautological test problem someone mentioned, i've found the easiest fix is to literally make the test fail first before letting the agent fix it

like don't ask it to "write tests for this function", instead give it a function that's deliberately broken in a specific way, make it write a test that catches that bug, verify the test actually fails, THEN fix the function

this forces the test to be meaningful because it has to detect a real failure mode. if the agent can't make the test fail by breaking the code, the test is useless

the other thing that helps is being really specific about edge cases upfront. instead of "write tests for this API endpoint", say "write tests that verify it returns 400 when the email field is missing, returns 409 when the email already exists, returns 422 when the email is malformed" etc

agents are weirdly good at implementing specific test scenarios but terrible at figuring out what scenarios actually matter. which honestly is the same problem junior devs have lol