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Why You Should Write Your Own Test Runner

When building mini projects, I often end up writing my own test framework. Here's why:

Benefits of Writing Your Own Test Runner​

  1. Learning Opportunity
    Writing a test runner helps you deeply understand the mechanics of testing. You’ll grasp concepts like test isolation, assertions, and setup/teardown processes more intuitively by implementing them yourself.

  2. Natural Extension of Application Growth
    As your application gains more structure, you can shift from testing entire pieces of the application to testing individual functions. Writing your own test runner aligns with this progression.

  3. No Overhead
    Established testing libraries come with learning curves—understanding different assert functions, patterns for table tests, and configuration requirements. When you write your own runner, you control everything. You can write it exactly the way you want without needing to adapt to external patterns.

  4. Flexibility
    You’re not constrained by the conventions of a testing library. Whether you want custom assertion messages, a unique test output format, or specific test flows, you can build exactly what you need.

When Established Tools Are Better​

For teams, using established tools like Jest, Mocha, or PyTest has clear benefits:

  • Consistency across team members.
  • Broad support and documentation.
  • Integration with CI/CD pipelines and other tools.

But for solo projects or experiments, writing your own test runner can be a valuable learning exercise and a great way to keep your projects lightweight.