What level of test coverage do you consider sufficient?

The optimal level of test coverage depends on the project, but generally aims for at least 70-80%. This ensures sufficient testing of core functionalities and reduces the likelihood of errors. It is important to cover critical and complex parts of the code, as well as business logic, with tests. However, 100% coverage is not always justified if tests become overly complex or do not provide value.

For example, in a Python project, you can use pytest and coverage.py to measure coverage and focus on unit testing key functions and methods.