Unit testing should be performed by developers. The testing rules are standard for all unit-testing on any features.
Unit Testing includes
- sunny cases (all good),
- rainy cases (bad input resulting error handling) and
- border/edge cases (like input is 0 or upper limit)
The above should be tested in different environments . For web Apps, features should be tested on different browsers – including IE, Chrome, Safari, both mobile and desktop.
For desktop app new features should be tested on common OS – Windows and Mac.
If during your unit testing you find an existing issue, then the developer could fix it if no one (customer) is using that feature. Alternatively, the developer could open a jira to track the issue.
After unit testing, the next stage is system or integration tests – which is done in a live data sample (e.g. demo).