Jest test fails : TypeError: window.matchMedia is not a function
This is my first front-end testing experience. In this project, I'm using Jest snapshot testing and got an error TypeError: window.matchMedia is not a function
inside my component.
I go through Jest documentation, I found the "Manual mocks" section, but I have not any idea about how to do that yet.
Solution 1:
The Jest documentation now has an "official" workaround:
Object.defineProperty(window, 'matchMedia', {
writable: true,
value: jest.fn().mockImplementation(query => ({
matches: false,
media: query,
onchange: null,
addListener: jest.fn(), // Deprecated
removeListener: jest.fn(), // Deprecated
addEventListener: jest.fn(),
removeEventListener: jest.fn(),
dispatchEvent: jest.fn(),
})),
});
Mocking methods which are not implemented in JSDOM
Solution 2:
I've been using this technique to solve a bunch of mocking problems.
describe("Test", () => {
beforeAll(() => {
Object.defineProperty(window, "matchMedia", {
writable: true,
value: jest.fn().mockImplementation(query => ({
matches: false,
media: query,
onchange: null,
addListener: jest.fn(), // Deprecated
removeListener: jest.fn(), // Deprecated
addEventListener: jest.fn(),
removeEventListener: jest.fn(),
dispatchEvent: jest.fn(),
}))
});
});
});
Or, if you want to mock it all the time, you could put inside your mocks
file called from your package.json
:
"setupFilesAfterEnv": "<rootDir>/src/tests/mocks.js",
.
Reference: setupTestFrameworkScriptFile