ecmascript 6 - Unit tests isolation with jestjs -

what best way handle test isolation jest? want test es6 class static methods , mock methods not directly concerned unit test.

my class file :

class util {      static getfirstname() {         return "john";     }      static getlastname() {         return "doe";     }      static getfullname(){         return `${util.getfirstname()} ${util.getlastname()}`;     } } 

my test file :

import util '../src/util';  test("test getfullname", () => {     util.getfirstname = jest.fn().mockreturnvalue("mockfirstname");     util.getlastname = jest.fn().mockreturnvalue("mocklastname");      expect(util.getfullname()).tobe("mockfirstname mocklastname") });  test("test getfirstname", () => {     expect(util.getfirstname()).tobe("john") });  test("test getlastname", () => {     expect(util.getlastname()).tobe("doe") }); 

this way, 2 last tests fail because mocks set on first test still active.

assuming import statements being transpiled require, should able use resetmodules:

beforeeach(() => {     // clears require cache new module require'd     // before each test.     jest.resetmodules(); }); 

then in each test, you'll need require module:

test("name", () => {     const { default: util } = require("../src/util"); }); 

or if can use dynamic import syntax:

test("name", () => import("../src/util")     .then(({ default: util }) => {         expect(util.getfirstname()).tobe("john");     }) );