From my answer to another question, this can be simpler: The only requirement is to configure your test environment to Babel, and add the ECMAScript 6 transform plugin: Step 1: Add your test environment to .babelrc in the root of your project: { “env”: { “test”: { “plugins”: [“@babel/plugin-transform-modules-commonjs”] } } } Step 2: Install the … Read more
Change .mockReturnValue with .mockImplementation: yourMockInstance.mockImplementation(() => { throw new Error(); }); in case you want to assert test(‘the fetch fails with an error’, () => { return expect(fetchData()).rejects.toMatch(‘error’); }); If it’s a promise you can also to .rejects www.jestjs.io/docs/en/asynchronous#resolves–rejects
In case, if you are accessing your application with a http://localhost prefix, you need to update your jest configuration (in your jest.config.js) as, “jest”: { “verbose”: true, “testURL”: “http://localhost/” } In case you do not already have any jest configuration, just include the configuration in your package.json. For example: { “name”: “…”, “description”: “…”, … … Read more
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
I’m using Visual Studio Code as my IDE and in my Angular project, and I had to comment-out/remove types in file tsconfig.json and add “jest” in types in tsconfig.spec.json. File tsconfig.json { “compilerOptions”: { // “types”: [] } } File tsconfig.spec.json { “compilerOptions”: { “types”: [“jest”, “node”] } }
describe breaks your test suite into components. Depending on your test strategy, you might have a describe for each function in your class, each module of your plugin, or each user-facing piece of functionality. You can also nest describes to further subdivide the suite. it is where you perform individual tests. You should be able … Read more
Just use mockObject.calls. In my case I used: const call = mockUpload.mock.calls[0][0] Here’s the documentation about the mock property
Use jest.requireActual() inside jest.mock() jest.requireActual(moduleName) Returns the actual module instead of a mock, bypassing all checks on whether the module should receive a mock implementation or not. Example I prefer this concise usage where you require and spread within the returned object: // myModule.test.js import { otherFn } from ‘./myModule.js’ jest.mock(‘./myModule.js’, () => ({ …(jest.requireActual(‘./myModule.js’)), … Read more
You can use type casting and your test.ts should look like this: import * as dep from ‘../dependency’; jest.mock(‘../dependency’); const mockedDependency = <jest.Mock<typeof dep.default>>dep.default; it(‘should do what I need’, () => { //this throws ts error // Property mockReturnValueOnce does not exist on type (name: string)…. mockedDependency.mockReturnValueOnce(‘return’); }); TS transpiler is not aware that jest.mock(‘../dependency’); … Read more
The following method worked for me. This approach allowed me to test some code that should work both in the browser and in Node.js, as it allowed me to set window to undefined. This was with Jest 24.8 (I believe): let windowSpy; beforeEach(() => { windowSpy = jest.spyOn(window, “window”, “get”); }); afterEach(() => { windowSpy.mockRestore(); … Read more