lukemorales / jest-type-matchers

Custom jest matchers to test the state of your types

jest-type-matchers

Custom jest matchers to test the state of your types.

You write Typescript and want assert various things about the state of your types?
This library provides a set of custom matchers that you can use to extend jest
and assert your test results against expected types.

📦 Install

This library is available as a package on NPM, install with your favorite package manager:

npm install --save-dev @lukemorales/jest-type-matchers

⚡ Quick start

Import @lukemorales/jest-type-matchers once in your tests setup file:

// In your jest-setup.ts (or any other name)
import '@lukemorales/jest-type-matchers';

// In jest.config.js add (if you haven't already)
setupFilesAfterEnv: ['<rootDir>/jest-setup.ts']

Custom Matchers

These custom matchers allow you to just check your types. This means that they will never fail your test suite because type-checking happens at compile-time only.

toHaveType

expect(true).toHaveType<boolean>();

type Result = { ok: boolean } & { data: null };

expect<Result>({ ok: true, data: null }).toHaveType<{ ok: boolean; data: null }>();

This allows you to check that a variable has an expected type.

toNotHaveType

expect('hello world').toNotHaveType<number>();

This allows you to check that a variable does not have a specific type.

toHaveStrictType

expect(true).toHaveStrictType<boolean>();

type Result = { ok: boolean } & { data: null };

expect<Result>({ ok: true, data: null }).toHaveStrictType<{ ok: boolean } & { data: null }>();

This allows you to check that a variable is strict equal to an expected type.

toNotHaveStrictType

expect('hello world').toNotHaveStrictType<number>();

This allows you to check that a variable is not strict equal to a specific type.