You can mock with a spy and import the mocked module. In your test you set how the mock should behave using mockImplementation: jest.mock(‘the-package-to-mock’, () => ({ methodToMock: jest.fn() })); import { methodToMock } from ‘the-package-to-mock’ it(‘test1’, () => { methodToMock.mockImplementation(() => ‘someValue’) }) it(‘test2’, () => { methodToMock.mockImplementation(() => ‘anotherValue’) })
Only methods can be spied. There is no way to spy on funcB if it’s called directly like funcB() within same module. In order for exported function to be spied or mocked, funcA and funcB should reside in different modules. This allows to spy on funcB in transpiled ES module (module object is read-only in … Read more
I was having the same failure (also using Babel, Typescript and Jest), it was driving me crazy for hours! Ended up creating a new babel.config.js file specifically for the tests. I had a large .babelrc that wasn’t getting picked up by jest no matter what I did to it. The main app still uses the … Read more
I was struggling with the same problem and actually it turns out that a simple change seems to do the trick. I just updated the moduleDirectories field in jest.config.js. Before moduleDirectories: [‘node_modules’] After moduleDirectories: [‘node_modules’, ‘src’]
The way I did it can be found in this Stack Overflow question. It is important to use resetModules before each test and then dynamically import the module inside the test: describe(‘environmental variables’, () => { const OLD_ENV = process.env; beforeEach(() => { jest.resetModules() // Most important – it clears the cache process.env = { …OLD_ENV … Read more
This error throws in useNavigate. useInRouterContext will check if the component(which uses useNavigate hook) is a descendant of a <Router>. Here’s the source code to explain why you can’t use useNavigate, useLocation outside of the Router component: useNavigate uses useLocation underly, useLocation will get the location from LocationContext provider. If you want to get the … Read more
You can test your async function like this: it(‘should test async errors’, async () => { await expect(failingAsyncTest()) .rejects .toThrow(‘I should fail’); }); ‘I should fail’ string will match any part of the error thrown.
I was struggling with the same problem and actually it turns out that a simple change seems to do the trick. I just updated the moduleDirectories field in jest.config.js. Before moduleDirectories: [‘node_modules’] After moduleDirectories: [‘node_modules’, ‘src’] Hope it helps.
Using jest.spyOn() is the proper Jest way of mocking a single method and leaving the rest be. Actually there are two slightly different approaches to this. 1. Modify the method only in a single object import Person from “./Person”; test(‘Modify only instance’, () => { let person = new Person(‘Lorem’, ‘Ipsum’); let spy = jest.spyOn(person, … Read more
As every test suite run its own environment, you can mock globals by just overwriting them. All global variables can be accessed by the global namespace: global.navigator = { onLine: true } The overwrite has only effects in your current test and will not effect others. This also a good way to handle Math.random or … Read more