Javascript jest

A test framework for javascript.

Documentation

intro	https://jestjs.io/docs/getting-started
home	https://jestjs.io/
assertions	https://jestjs.io/docs/expect#expect

Usage

General

./node_modules/.bin/jest \
  --no-coverage \
  --colors                      `# force colours` \
  -t $DESCRIBE_REGEX $IT_REGEX  `# regex match tests` \
  $TEST_FILEPATH

Debugger Statements

Run tests, with interactive repl for debugger; statements where you've entered them in your code.

# 1. run test, with server on port 9330 (one variant of these)
node --inspect-brk=9330 ./node_modules/jest/bin/jest.js --runInBand some/test.js
# OR
NODE_OPTIONS='--unhandled-rejections=warn --inspect-brk=9330' jest --runInBand some/test.js


# 2. connect to the server in a separate nodejs process
node inspect 127.0.0.1:9330

# 3. use one of the provided commands
help  # show commands

// note that:
//   - logging will occur in the test-runner process
//   - you'll be at a prompt until you hit a breakpoint in the server
list()          // show current place in stack
repl            // enter stack, allow you to 'console.log()' variables
.exit / ctrl-c  // exit 'repl'

Basics

// ${project}/foo.js

function sum(a, b) { return a + b; }

// ${project}/foo.test.js

const sum = require('./foo.js');

test('1 + 2 is 3', () => {
    expect(sum(1, 2)).toBe(3);
})

Features

Only (focus)

only lets you focus/run just a single test from the file.

it.only('does thing', () => {
  expect(true).toBe(false)
  })

Each (parametrize tests)

test.each([
  [1, 1, 2],
  [1, 2, 3],
  [2, 1, 3],
])('adds %i + %i to equal %i', (a, b, expected) => {
  expect(a + b).toBe(expected);
});

beforeEach / afterEach hooks

let user: User;

beforeEach(() => {
  user = new User();
});

it('has a name', () => {
  expect(user.name).toBe('foouser');
});

Expect Exceptions

// regular functions
expect(() => {
  throw new TypeError('Wrong type');
}).toThrow(TypeError);

// async functions
await expect(async () => {
  throw new Error('Async error');
}).rejects.toThrow('Async error');
// or
await expect(someAsyncFunction()).rejects.toThrow();

Mocks

SpyOn

const mySpy = jest.spyOn(some.obj, 'someFunction');
expect(myspy).toHaveBeenCalled();
expect(myspy).toHaveBeenCalledWith(1, 2, 3);

const mod = require('some/module');
const modSpy = jest.spyOn(mod, 'someFunction');

Replace the function's behaviour

// for regular functions
const spyStringify = jest
  .spyOn(JSON, 'stringify')
  .mockImplementation(() => throw Error('oh no!'));

// for async functions
const spyFoo = jest
  .spyOn(myMod, 'someAsyncFunc')
  .mockRejectedValue(new Error('oh no!'));

const spyFoo = jest
  .spyOn(myMod, 'someAsyncFunc')
  .mockResolvedValue('success!');