Testing generators are verbose as they require calling next method of generator each time you want to iterate. jest-generator encapsulates all iteration and assertion logic itself. It provides easy and readable API for testing generator functions.

Installation

yarn add --dev jest-generator

or

npm install --save-dev jest-generator

Setup

Via setupTestFrameworkScriptFile config

Add jest-generator to your Jest setupTestFrameworkScriptFile configuration

"jest": {
  "setupTestFrameworkScriptFile": "jest-generator"
}

Via setupTest script

Require jest-generator from setupTest script

// ./setupTest.js

require('jest-generator');

Then add this config

"jest": {
  "setupTestFrameworkScriptFile": "./setupTest.js"
}

Usage

// ./pay.js

export default function* pay() {
  yield validatePayment();
  yield makePayment();

  return finishPayment();
}

// ./pay.test.js

import pay from './pay';

test('should work correctly', () => {
  const iterator = pay();

  expect(iterator).toMatchYields([
    [validatePayment()],
    [makePayment()],
    [finishPayment()]
  ]);
});

Usage with other libraries

Usage with Saga

// ./books.js

export function* loadBooks(params) {
  try {
    const response = yield call(api.loadBooks, params)
    
    yield put(booksLoadedSuccess(response))
  } catch (error) {
    yield put(booksLoadFail(error.message))
  }
}

// ./books.test.js

import { loadBooks } from './books';

test('should handle success response', () => {
  const params = { id: 201 };
  const iterator = loadBooks(params);
  const response = [];

  expect(iterator).toMatchYields([
    [call(api.loadBooks, params), response],
    [booksLoadedSuccess(response)],
  ]);
});

test('should handle error response', () => {
  const params = { id: 201 };
  const iterator = loadBooks(params);
  const response = new Error('failed to load books');

  expect(iterator).toMatchYields([
    [call(api.loadBooks, params), response],
    [put(booksLoadFail(response.message))],
  ]);
});

API

.toMatchYields(
  yieldValues: [
    [yieldValue: any, returnType?: any | Error]
  ]
)

Matches iterator against given yield values

expect(iterator).toMatchYields([
  [callAPI()]
])

In order to return value from yield, simply pass your return value as second array value

function* gen() {
  const response = yield fetch()
  yield update(response)
}

const mockResponse = {};
const iterator = gen();

expect(iterator).toMatchYields([
  [fetch(), mockResponse],
  [update(mockResponse)]
])

In order to throw error from yield, you should simply pass Error instance to return type

function* gen() {
  const response = yield fetch()
  yield update(response)
}

const mockErrorResponse = new Error('network error');
const iterator = gen();

expect(iterator).toMatchYields([
  [fetch(), mockErrorResponse],
  [handleError(mockErrorResponse)]
])

Licence

This project is licensed under the MIT License - see the LICENSE file for details