Jest cheat sheet

jest.md

Jest cheat shiiiit

Expect

expect.any(constructor) // expect(callback).toBe(expect.any(Function))
expect.assertions(number) // total count of expected assertions, useful for async tests
.not
.resolves
.rejects
.toBe(value)
.toHaveBeenCalled()
.toHaveBeenCalledTimes(number)
.toHaveBeenCalledWith(arg1, arg2, ...)
.toHaveBeenLastCalledWith(arg1, arg2, ...)
.toBeCloseTo(number, numDigits)
.toBeDefined()
.toBeFalsy()
.toBeGreaterThan(number)
.toBeGreaterThanOrEqual(number)
.toBeLessThan(number)
.toBeLessThanOrEqual(number)
.toBeInstanceOf(Class)
.toBeNull()
.toBeTruthy()
.toBeUndefined()
.toContain(item)
.toContainEqual(item)
.toEqual(value)
.toHaveLength(number)
.toMatch(regexpOrString)
.toMatchObject(object)
.toHaveProperty(keyPath, value)
.toMatchSnapshot(optionalString)
.toThrow(error)
.toThrowErrorMatchingSnapshot()

Jest object

Standard spy

const callback = jest.fn(() => "mock return value"); // function is optional
callback(1);
callback(2);
expect(callback).toHaveBeenCalledTimes(2);
expect(callback.mock.calls[callIndex][argIndex]).toEqual(...);

Spy on object method

const spy = jest.spyOn(object, 'objectMethod');
object.objectMethod();
expect(spy).toHaveBeenCalled();

spy.mockReset(); // resets spy
spy.mockRestore(); // resets original method IMPORTANT for cleanup eg. mocking window

Spy and override method

jest.spyOn(object, 'methodName').mockImplementation(() => 'my value');
jest.spyOn(object, 'methodName')
    .mockImplementationOnce(() => 'first call')
    .mockImplementationOnce(() => 'second call'); // can be called on jest.fn() too

Timers

jest.useFakeTimers();
jest.runTimersToTime(500); // ms
jest.clearAllTimers();

Jest object API

jest.clearAllTimers()
jest.isMockFunction(fn)
jest.genMockFromModule(moduleName)
jest.mock(moduleName, factory, options)
jest.clearAllMocks()
jest.resetAllMocks()
jest.resetModules()
jest.runAllTicks()
jest.runAllTimers()
jest.runTimersToTime(msToRun)
jest.runOnlyPendingTimers()
jest.setMock(moduleName, moduleExports)
jest.unmock(moduleName)
jest.useFakeTimers()
jest.useRealTimers()

Configuration

Polyfills

Request animation frame

yarn add --dev raf

// jest.setup.js
const raf = require('raf');
raf.polyfill();

// package.json
"jest": {
    ...
    "setupTestFrameworkScriptFile": "<rootDir>/jest.setup.js",
    ...
}