eslint-plugin-ts-expect

Write dtslint style comment assertions using eslint.

Setup

If you do not already have an eslint setup using eslint-plugin-typescript, follow the instructions for configuring that first.

Once your project is setup to use eslint with typescript:

yarn add -D eslint-plugin-ts-expect

Then setup the plugin and rule as you might for any other eslint rule. In your .eslintrc.json:

// tests/.eslintrc.js

module.exports = {
  parser: '@typescript-eslint/parser',
  parserOptions: {
    tsconfigRootDir: __dirname,
    project: ['./tsconfig.json'],
  },

  plugins: ['ts-expect'],
  rules: {
    'ts-expect/expect': 'error',
  },
};

Note: These rules require type information to work so you may need to follow these additional steps to enable type checking rules

You can write assertions in any file that has the rule enabled, though you probably want to scope it to test files.

Usage

const add = (a: number, b: number): number => a + b;

// $ExpectType number
add(1, 1);

// Also works on the next line
add(2, 3); // $ExpectType number

// $ExpectError
add('one');

// $ExpectError
add(1);