Modern application development depends on tests. The software development life cycle has evolved to take a test-first approach, with tests designed from the same requirements as your code. At the heart of this model is the unit test, ensuring that each module of your code responds to inputs correctly and delivers the expected outputs.
That requires developing tests before you even write your first line of code, providing a framework that ensures that all code in a CI/CD (continuous integration and continuous delivery) system has passed functional tests before being assembled into an application or service. This test-first approach is central to agile development methodologies, giving sprints a target that can measure progress.