1 agent writes the tests, threads the needle.

Another agent reviews the tests, finds duplicate code, finds poor testing patterns, looks for tests that are only following the "happy path", ensures logic is actually tested and that you're not wasting time testing things like getters and setters. That agent writes up a report.

Give that report back to the agent that wrote the test or spin up a new agent and feed the report to it.

Don't do all of this blindly, actually read the report to make sure the llm is on the right path. Repeat that one or two times.