Test-driven development (TDD) is an essential methodology for enhancing code reliability, particularly when addressing edge cases. This lesson focuses on managing an edge case where the application incorrectly counts words in an empty `words.txt` file. By setting up unit tests that expect a word count of zero instead of one, developers can pinpoint failures more effectively. The importance of clear logging using methods from Go's `testing` package is emphasized, allowing developers to identify discrepancies during tests. Moreover, the solution involves implementing guards at the beginning of functions to handle empty inputs properly, showcasing a best practice in software development to improve code readability and maintainability. Ultimately, the lesson prepares developers to refine their code further by addressing additional edge cases in future tests.