testing

Testing Software

Verification Loop First

Give every change a check it can run before calling it done: red-then-green for new logic, a failing-then-passing regression test for bug fixes, or the existing suite for anything else. No change ships without one.

Red-green-observe, not red-green-assume: "confirm it fails" (the Regression workflow item below, and TDD's "watch it fail" step) means actually run the test and read the failure output before touching the fix or the implementation — never reason your way to "this must fail" and skip the run.

Falsifiable done-when: before writing a feature's implementation, state one concrete, checkable condition that defines done — not "should work now," a condition a test or command can confirm or refute.

Evidence over narration: a completion claim is only as good as what it cites — a pasted test-run result, a real exit code, a pushed commit SHA. Describing what the code should now do is not evidence; re-running the check and quoting its output is.

MCP Tools

Chrome DevTools (E2E testing):

• Automate user flows in real browser
• Capture screenshots for visual regression
• Run Lighthouse for accessibility testing
• Profile performance during test runs

Workflow

• Analyze: Use Glob and Grep to identify untested code
• Unit Tests: Cover all public functions
• Edge Cases: Test boundaries and error conditions
• Integration: Test external dependencies
• E2E: Use Chrome DevTools for browser automation
• Regression: Add a test that reproduces the bug, confirm it fails against the current code, then fix — keep it passing and in the suite afterward (never delete or skip it)

Test-Driven Development

When writing new logic, default to red-green-refactor:

1. Red: Write a failing test for one behavior before writing the implementation.
2. Green: Write the minimum code needed to make that test pass.
3. Refactor: Clean up structure only while the suite is green — no new behavior in this step.

• One behavior per test — if a test needs "and" to describe it, split it.
• Never write production code without a failing test driving it, except for spikes/throwaway exploration (delete or backfill tests before merging).
• Don't refactor and add behavior in the same commit; commit on green before switching hats (see code-quality.md Two Hats Rule).

When TDD is the right default: new business logic, bug fixes (write the regression test first, watch it fail, then fix), and any code with clear input/output contracts.

When it isn't: exploratory spikes, throwaway scripts, UI layout/styling tweaks, and generated boilerplate — write tests after the shape stabilizes instead.

Test Quality Standards

Deterministic

Tests must produce the same result every time — no reliance on wall-clock time, random values, or uncontrolled external state.

Isolated

Tests must not depend on each other or share mutable state.

Clear

Test names describe the behavior under test, not just the function name.