What characterizes test-driven development (TDD)?

Test-driven development (TDD) is characterized primarily by the practice of writing test cases before the corresponding code is developed. This approach ensures that the developer has a clear understanding of the expected behavior of the code before it is written, promoting better design and functionality. By starting with tests, developers can specify the requirements and expectations of the code, leading to more structured and reliable development.

This method also encourages iterative development; as each new test is written to validate a specific functionality, the code is then created or modified to pass these tests. This cycle of writing a test, writing just enough code to pass the test, and then refactoring the code aligns with the core principles of TDD, leading to fewer bugs and a more robust codebase.

The other options do not accurately capture the essence of TDD. For example, writing tests after the code is developed contradicts TDD's foundational principles, and automation of test scenarios, while beneficial, is not a defining characteristic of TDD itself. Additionally, focusing solely on user interface design is not relevant to the broader process of TDD, which encompasses the development of all aspects of the software.