Test-Driven Development: Writing Robust Code with Unit Tests

Test-driven development (TDD) is an agile software development technique where you write unit tests before writing the actual code. The basic process is as follows:

Write a test that fails because the code needed to pass the test doesn't exist yet. This ensures that you know exactly what needs to be coded.
Write the minimum amount of code necessary to make the test pass. This means writing small, focused code.
Refactor your new code to clean it up without breaking the tests. The tests act as a safety net during refactoring.
Repeat this cycle—Red, Green, Refactor—continuously so each small functionality added is tested immediately.

Some benefits of TDD are:

Robust code: The tests act as specifications that must be met before shipping the code. This reveals errors early.
Self-documenting: The tests themselves clearly show how the code should behave.
Faster iterations: Writing tests first clarify what exactly needs to be coded.
Flexible: Changes can be made quickly without breaking existing functionality.
Decreased technical debt: bugs get found and fixed immediately instead of piling up.

Here are a few tips for writing good tests:

Test one thing per test; keep your tests focused.
Name tests clearly to indicate what functionality they test.
Test edge cases, invalid inputs, and success/failure conditions.
Use mocking to isolate your tests from a single unit of code.
Aim for 100% code coverage with your test suite.

The key is to adopt a mentality of "tests first, code second." Build up your codebase in short cycles of tests and functionality.

This results in clean, robust, flexible code that's easy to maintain and extend.