In my experience in QA, I performed manual and automated test cases both formally and informally. Informal testing was usually done before formal testing to see and issues or defects that arose – test cases were executed but evidence of successfully passing test cases weren’t documented in informal testing. In formal testing most steps require evidence of passing required by the FDA. Formal testing also required documentation of all tools used and information of the person running the test case.
I have also performed “monkey” testing where as a tester I use the device/software and try to generate any issues as a user without a set test plan.