Mocking require statements with Jest

Question

sum.js

module.exports = function sum(a, b){     return a + b; }; 

Thing.js

var sum = require("./sum");  module.exports = class Thing {     add(a, b){         return sum(a, b);     } } 

Thing.test.js

test('1 + 2 = 3', () => {     //Arrange     var Thing = require('./Thing');     var thing = new Thing();      //Act     var result = thing.add(1, 2);      //Assert     expect(result).toBe(3); });  test('sum mocked', () => {     //Arrange     jest.mock('./sum', () => {         return jest.fn(() => 42);     });      var Thing = require('./Thing');     var thing = new Thing();      //Act     var result = thing.add(1, 2);      //Assert     expect(result).toBe(42); }); 

How can I mock the sum 'require' dependency when testing? I get the following error.

sum mocked      expect(received).toBe(expected)      Expected value to be (using ===):       42     Received:       3 

What's interesting if I run each test individually with .only, they both work just fine on their own.

In the past I've used proxyquire to do things like this but I'd like to avoid it if possible.

Answer 1

In the test, I added

beforeEach(() =>  {     jest.resetModules(); }); 

and the tests passed as expected.