How to Mock Functions Within the Same Module Using Jest?

Mocking Functions Within the Same Module in Jest

To mock functions within a module using Jest, the recommended approach is to import the module into its own code file. This allows for easier mocking of functions within the module.

Consider the following example:

// module.js
export function bar() {
    return 'bar';
}

export function foo() {
    return `I am foo. bar is ${bar()}`;
}

In the corresponding test file, mocking bar can be simplified by importing the module into its own code file:

// module.test.js
import * as thisModule from './module';

describe('module', () => {
    it('foo', () => {
        spyOn(thisModule, 'bar').and.returnValue('fake bar');
        expect(thisModule.foo()).toEqual('I am foo. bar is fake bar');
    });
});

In this approach, foo references the imported instance of bar, making it straightforward to mock bar for testing purposes.

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