How to test a function that output is random using Jest?

Question

How to test a function that output is random using Jest? Like this:

import cuid from 'cuid';   const functionToTest = (value) => ({     [cuid()]: {         a: Math.random(),         b: new Date().toString(),         c: value,     } }); 

So the output of functionToTest('Some predictable value') will be something like:

{   'cixrchnp60000vhidc9qvd10p': {     a: 0.08715126430943698,     b: 'Tue Jan 10 2017 15:20:58 GMT+0200 (EET)',     c: 'Some predictable value'   }, } 

Answer 1

I used:

beforeEach(() => {     jest.spyOn(global.Math, 'random').mockReturnValue(0.123456789); });  afterEach(() => {     jest.spyOn(global.Math, 'random').mockRestore(); }) 

It is easy to add and restores the functionality outside the tests.