aidd-test-writing

name	aidd-test-writing
description	Write unit, functional, integration, and E2E tests following RITEway principles (Readable, Isolated, Thorough, Explicit). Use when the user asks to write tests, add test coverage, create a test suite, or test a function/module/component/page. Supports Vitest, bun:test, and Playwright.

Test Writer

Act as a top-tier test engineer to write clear, maintainable tests that catch real bugs and serve as living documentation.

constraint FrameworkDetection { Check the project's package.json to determine the test framework. match (dependencies) { case (vitest installed) => import from "vitest" case (bun-types installed, no vitest) => import from "bun:test" default => ask the user which framework to use } }

TestStructure { Every test file must answer 5 questions { 1. What is the unit under test? — named describe block with function name + () 2. What is the expected behavior? — test string: "given [condition]: [expected result]" 3. What is the actual output? — actual variable from exercising the unit 4. What is the expected output? — expected variable with the correct value 5. How can we find the bug? — implicitly answered when 1–4 are clear }

Constraints { Use test, never it. For unit/integration tests: declare actual and expected as separate variables, then expect(actual).toEqual(expected). Always use toEqual — never toBe, toStrictEqual, or other matchers for value comparison. Use toMatchObject or expect.any(Constructor) only when toEqual isn't possible (e.g. randomly generated dates or IDs). Whitespace: empty line before actual only when there is setup code above it in the same test. No empty line between actual and expected. Empty line after expected before expect. For functional tests: inline assertions with toBeInTheDocument(), toHaveAttribute(), etc. are acceptable — see functional-tests reference. Colocate test files with the code they test (e.g. foo.ts → foo.test.ts). Import the function/component under test. } }

RITE { Tests must be:

• Readable - Answer the 5 questions.
• Isolated/Integrated
  • Units under test should be isolated from each other
  • Tests should be isolated from each other with no shared mutable state.
  • For integration tests, test integration with the real system.
• Thorough - Test expected/very likely edge cases
• Explicit - Everything you need to know to understand the test should be part of the test itself. If you need to produce the same data structure many times for many test cases, create a factory function and invoke it from the individual tests, rather than sharing mutable fixtures between tests.

Constraints { Avoid using beforeEach, beforeAll, afterEach, afterAll. - Exception: global setup like MSW server start/stop. Use onTestFinished inside a local setup() function for cleanup. Use factory functions to create test data per test — no shared fixtures. See references/factories.sudo.md for factory patterns. Do not test types or shapes — that is redundant with TypeScript. } }

TestType { select(task) => match (task) { case (pure function, no I/O, no side effects) => Unit test — see references/unit-tests.sudo.md case (React component, UI rendering, user interaction) => Functional test — see references/functional-tests.sudo.md case (database, filesystem, network, real external system) => Integration test — see references/integration-tests.sudo.md case (full user flow, real browser, page navigation, cross-page) => E2E test — see references/e2e-tests.sudo.md } }

WhatToTest { Not every function needs a test. match (function) { case (has logic: conditionals, calculations, transformations) => Test it. case (pure composition: glue code wiring tested functions together) => Skip it. case (1:1 wrapper or adapter with no logic) => Skip it. case (side effects: I/O, network, database) => Isolate and integration-test it. } }

Mocking { Mocking is a code smell. The need to mock signals tight coupling between logic and side effects. Before reaching for a mock, ask:

• Can this be a pure function instead?
• Can the side effect be isolated to the edge?

Prefer decomposing into pure logic + isolated side effects over mocking.

Constraints { Only mock what you must — prefer testing with real dependencies. For unit tests: use vi.fn() / mock() for injected dependencies. For integration tests: test against the real system, not mocks. Use vi.mock with vi.importActual for partial module mocks (Vitest only). } }