twake-frontend-testing

name	twake-frontend-testing
description	Use when writing, reviewing, or refactoring frontend tests in Twake/Cozy React projects. Enforces @testing-library/react (never Enzyme or TestCafe), data-testid attributes, queryBy + toBeInDocument()/toBe(null) patterns, colocated *.spec files (no __tests__ folders), and bans snapshot tests.

Frontend Testing (Twake / Cozy)

Apply these rules when writing or reviewing any frontend test in a Twake or Cozy React project.

Test library

• Use @testing-library/react.
• Do not use Enzyme. It is deprecated in Cozy / Twake projects.
• Do not use TestCafe. Also deprecated.

If you find legacy Enzyme or TestCafe tests while editing nearby code, leave them alone unless migration is the task at hand — migration is its own ticket.

No snapshot tests

Do not write toMatchSnapshot() / toMatchInlineSnapshot() tests. They rot silently: reviewers rubber-stamp regenerated snapshots, which defeats the point of a test.

Assert on explicit, meaningful properties instead:

// ❌ Forbidden
expect(container).toMatchSnapshot()

// ✅ Good
expect(screen.getByRole('heading')).toHaveTextContent('Welcome, Alice')
expect(screen.queryByTestId('error-banner')).toBe(null)

Selecting elements — data-testid

• Add a data-testid attribute on any element a test needs to target, if no accessible role / label already works.
• Prefer getByRole / getByLabelText first (better for accessibility). Fall back to data-testid only when the semantic query is ambiguous or fragile.
• Use kebab-case for test ids: submit-btn, error-banner.

queryBy vs getBy in assertions

Use the right helper for the right assertion:

Intent	Helper	Matcher
Element must be present	getByX	— (getByX throws if absent)
Assert presence explicitly	queryByX	.toBeInTheDocument()
Assert absence	queryByX	.toBe(null)

// ✅ Good
expect(screen.queryByTestId('submit-btn')).toBeInTheDocument()
expect(screen.queryByTestId('error-banner')).toBe(null)

// ❌ Avoid — passes even when the element doesn't render
expect(screen.getByTestId('submit-btn')).toBeDefined()

The .toBeDefined() pattern is a false positive: getByX throws on absence, so the matcher never actually runs the absent-case assertion.

File layout — colocate, don't segregate

Test files live next to the source file, not in a separate __tests__ folder.

components/
  UserCard.jsx
  UserCard.spec.jsx        ✅ colocated
  UserCard.styl

  __tests__/               ❌ do not create
    UserCard.jsx

Naming: <SourceFile>.spec.<ext> (e.g. UserCard.spec.jsx, formatAmount.spec.js).

What to test

• Cover the component's public behavior: what a user (or caller) can observe.
• Do not test implementation details: internal hooks, private helpers, specific render counts.
• One describe per component or module; one it per behavior. Keep test names human-readable (it('shows an error when the password is too short')).