Test-Driven Development (TDD)
Get feature changes, bug fixes, and refactors backed by behavior-focused tests and clear validation results.
Free
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Example session with this skill installed
Use TDD to write a JavaScript shippingFee(subtotal): $5 below $50, free at $50 or more. Reject negative amounts.
- Read your context and instructions
- Compiled the test-driven development tdd
Prepared the shipping fee implementation and tests for the requested behavior. Execution is unavailable here, so these checks are unrun, not verified passes.
Implementation and tests
Amounts are in dollars. Save the implementation as shipping.mjs.
export function shippingFee(subtotal) {
if (subtotal < 0) {
throw new RangeError('Subtotal cannot be negative');
}
return subtotal >= 50 ? 0 : 5;
}
Save the tests as shipping.test.mjs.
import test from 'node:test';
import assert from 'node:assert/strict';
import { shippingFee } from './shipping.mjs';
test('charges $5 below the free-shipping threshold', () => {
assert.equal(shippingFee(0), 5);
assert.equal(shippingFee(49.99), 5);
});
test('offers free shipping at $50 and above', () => {
assert.equal(shippingFee(50), 0);
assert.equal(shippingFee(75), 0);
});
test('rejects negative subtotals', () => {
assert.throws(() => shippingFee(-1), {
name: 'RangeError',
message: 'Subtotal cannot be negative'
});
});
Next steps
- Run
node --test shipping.test.mjswith a Node.js version that supportsnode:test. - Run the checkout tests after connecting this function to the order total.
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About this skill
Feature changes can break working code, and brittle tests can make cleanup harder than it should be. Get implementation changes backed by behavior-focused tests, with clear reporting on what was actually checked.
What it does
- Builds features with tests: Adds code and tests around the behavior your users or API consumers need.
- Fixes bugs with coverage: Tests the requested correction through a public interface.
- Restructures existing code: Refactors internals while checking that observable behavior stays the same.
- Reports validation evidence: Separates executed checks from checks that could not be run.
How it works
- Describe the feature, bug, or internal cleanup you want.
- Provide access to the repository, existing tests, and relevant project documentation.
- Review any questions about choices that affect business behavior or scope.
- Receive code changes, supporting tests, and a validation report.
Works with
Your project's existing code, public APIs, test runner, and quality checks. No particular programming language or framework is prescribed.
Why use this skill
Tests focus on observable results rather than private implementation details, reducing unnecessary test changes during refactoring. Repository conventions and documented contracts help keep changes consistent with the project. Validation reporting makes unverified work easier to spot.
Use cases
- Add a feature with tests for its critical behavior.
- Fix a regression and cover the corrected result.
- Extract tangled responsibilities without changing public behavior.
Known limitations
Executing checks requires a working project environment. Coverage is prioritized around risk and important behavior, not every possible edge case.
How to use
Skills on Agensi run inside your AI agent. Copy the prompt, paste it into your agent, and it connects to Agensi and installs this skill for you. If a payment is needed, your agent shows it to you first.
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