Jest

jestTesting36 lines

Unit and component testing. Adapts its configuration to the platform you selected.

Current — as published in v1.3.2. Written by hand for Jest, not generated.

The rule

Queries

Find elements the way a user does: getByText, getByLabelText, getByRole.
getByTestId is a last resort. Reaching for it first produces tests that pass while the screen is unusable by anyone relying on a screen reader.
Anything async uses findBy*, which retries. getBy* does not, and a fixed setTimeout to compensate is a flake waiting to happen.

Mocking

Mock native modules and third-party SDKs in jest.setup.js.
Where this project wraps an SDK in a service, mock the service.
Never mock your own modules to make a test pass — that couples the test to the current file layout and it will break on a no-op refactor.
Reset mocks in beforeEach. A test that only passes in isolation is broken.

Structure

it('surfaces a retryable error when the token has expired', async () => {
  // arrange — the least setup that makes the scenario true
  // act     — one interaction
  // expect  — what a caller or user observes
});

One reason to fail per test, and a name that says which.

Do not

Do not commit it.only or it.skip.
Do not add snapshots nobody reads.
Do not test library behaviour — test this project's use of it.
Do not chase a coverage percentage; cover the paths that can be wrong.

As each tool receives it

The same guidance, in the shape each editor reads. Cursor and Claude Code are written separately by hand; the rest are derived from the Cursor rule.

→ .cursor/rules/jest.mdchand-written for this tool

.cursor/rules/jest.mdc

---
description: Jest and React Native Testing Library conventions
globs: ["**/*.test.ts", "**/*.test.tsx", "**/__tests__/**", "jest.setup.js"]
alwaysApply: false
---

# Jest

## Queries

- Find elements the way a user does: `getByText`, `getByLabelText`, `getByRole`.
- `getByTestId` is a last resort. Reaching for it first produces tests that pass
  while the screen is unusable by anyone relying on a screen reader.
- Anything async uses `findBy*`, which retries. `getBy*` does not, and a fixed
  `setTimeout` to compensate is a flake waiting to happen.

## Mocking

- Mock native modules and third-party SDKs in `jest.setup.js`.
- Where this project wraps an SDK in a service, mock the **service**.
- Never mock your own modules to make a test pass — that couples the test to
  the current file layout and it will break on a no-op refactor.
- Reset mocks in `beforeEach`. A test that only passes in isolation is broken.

## Structure

```ts
it('surfaces a retryable error when the token has expired', async () => {
  // arrange — the least setup that makes the scenario true
  // act     — one interaction
  // expect  — what a caller or user observes
});
```

One reason to fail per test, and a name that says which.

## Do not

- Do not commit `it.only` or `it.skip`.
- Do not add snapshots nobody reads.
- Do not test library behaviour — test this project's use of it.
- Do not chase a coverage percentage; cover the paths that can be wrong.

What else this module writes

Selecting Jest contributes more than a rule file — all of it merged with every other module you pick, with conflicts resolved rather than duplicated.

Dependencies

Depends on the rest of the stack — this module installs different packages depending on what else you select, so there is no single list to show.

Folders

src/test/factories/

Put this in your repo

Adds Jest to a project this tool generated, without starting over. Files you have hand-edited are left alone.