What common mistake do developers make with Factories in tests, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Factories in tests, why does the mistake cause problems, and what is the safer approach? One recurring problem with factories in tests is applying it without understanding the boundary it protects. Writing a test that only asserts a 200 response while never verifying that the important application state actually changed. In addition, Factories create realistic model state for tests without manually constructing every database record. Safer engineering approach: keep the responsibility in the correct layer, use the framework's supported API, validate and authorize inputs, avoid hidden side effects, and verify the behavior with tests.