test-driven-development
Implements a feature or bug fix test-first - write one failing test, watch it fail, write the minimal code to pass, then refactor with tests green. This is the implementation stage inside the delivery-flow workflow, entered by requests like "implement this feature", "fix this bug", "write the code for this", or "add the tests and implement it" once delivery-flow is driving the change. Do not activate directly for a standalone request that has not gone through delivery-flow first.
75
94%
Does it follow best practices?
Run evals on this skill
Adds up to 20 points to the overall score
Passed
No findings from the security scan
The canonical home for this skill is test-driven-development in tesslio/tessl-eval-demo
Test-Driven Development
Write the test first. Watch it fail. Write the minimal code to pass. Refactor with the tests green.
The cycle
- Red. Write one test for one behavior. Use a clear name and the real code, not mocks.
- Watch it fail. Run the project's test command. The test must fail because the behavior is missing, not because of a typo or a missing import. If it passes, it tests nothing new: change the test.
- Green. Write the simplest production code that makes it pass. Add nothing the test does not need.
- Watch it pass. Run the full suite. Every test passes, with no errors or warnings.
- Refactor. Clean up names and duplication. Run the suite again.
Repeat for the next behavior.
Rules
- No production code without a failing test first. Code written before its test is deleted and written again from the test.
- A bug fix starts with a test that reproduces the bug.
- If the test is hard to write, the design is unclear: simplify the interface.
- When writing or changing a test, read references/writing-good-tests.md.
Before you say it is done
- Each new behavior has a test that you saw fail first.
- The full suite passes on the final code.
- Last updated
- First committed
Canonical home
since Oct 13, 2026
Also appears in
since Oct 13, 2026
since Oct 13, 2026
since Oct 13, 2026
Is this your skill?
If you maintain this skill, you can claim it as your own. Once claimed, you can manage eval scenarios, bundle related skills, attach documentation or rules, and ensure cross-agent compatibility.