Tests

Reading

Avoid testing implementation details: https://kentcdodds.com/blog/testing-implementation-details

Text in the app may change as translators and copywriters update strings in Crowdin, independently of developers. To avoid failing tests in Crowdin sync PRs, get the string by its translation ID instead of using the literal text.

// bad
expect(
    screen.getByText('This can change with a Crowdin sync and someone will have to fix the test.'),
).toBeTruthy();

// good
expect(screen.getByText(getTranslation('path.to.translation'))).toBeTruthy();

// In case there is some string that must not be changed:
expect(screen.getByText(getTranslation('path.to.translation'))).toBe(
    'I want a developer to check this important text if it is changed in Crowdin.',
);

Naming conventions

Tests are placed in __tests__ folders and have .test.ts extension.
Test folder is placed in the same directory as an actual implementation.
When testing types, suffix should be .type-test.ts, to prevent from being executed by jest. (For example: packages/utils/tests/typedObjectFromEntries.type-test.ts)
Fixtures are placed in mocks folders and have mock prefix.
mocks folder is placed in the root of the package, not in src.

Example:

my-module/
├── mocks/
│   └── mockMyComponent.ts
└── src/
    ├── __tests__/
    │   └── utils.test.ts
    └── utils.ts

Reusability

To keep things simple, avoid creating complex mocks to be shared between multiple test suites. In case you do reuse a mock, keep it generic and non-opinionated.

Simple test: change in shared mock SHALL NOT break existing tests (or make fixes trivial).

Mocks (& Fixtures)

Typing

All fixtures and mocks shall be typed and declaratively defined; using as to cast an incomplete object is only a last resort. This may add boilerplate, but it ensures type changes surface as type errors instead of hard-to-fix failing tests.

Organization & Naming Convention

Mock/fixture files shall be placed in the same package where the subject being mocked resides.
Putting them in a types package is OK. A mock for Device shall be in the same package where the type declaration is located.
Use mock prefix to distinguish it from type or original implementation. Device => mockDevice.
Prefer factories to static objects. A factory is better because it can provide an API to create a mock with desired changes. (mockDevice(data: Partial<Device>): Device => ({ ... }))
Put mocks into a mocks directory within the same package.

Export them from the package via a separate file. In this example: import { mockDevice } from '@common/device-types/mocks'

device-types
  - mocks
     - mockDevice.ts
     - index.ts // If you need to export them in `package.json`
  - src
     - device.ts

Name the file the same as the exported mock.

Trezor Suite