Unit tests are the bread and butter of any project's quality assurance process. We software developers have been used to writing them and measuring code coverage in our continuous integration pipelines for years. There is tooling that helps us find untested areas, records the coverage percentages, and notifies us if the changes cause a drop in the test scope. Still, one can not test all features thoroughly with unit testing in all projects. Sometimes mocking the external functionality is so laborious that wasting the team's resources on creating the mock code doesn't make sense. Or it may even be impossible to reproduce the external functionality with the mockups.