Ways to imitate an export default function

//CustomConfigurator.ts
export default function customizeConfig(name: string): string {
  // add some custom logic here
  return output;
}
//CustomUtility.ts
import customizeConfig from './CustomConfigurator';

export default class CustomUtility {
  public static checkIfFoo(): boolean {
    const customizedConfig = customizeConfig();
    return customizedConfig == 'Foo';
  }
}
//CustomUtility.test.ts
import CustomUtility from '../CustomUtility';
import * as customConfig from '../CustomConfigurator';

const configMock = customConfig.default as jest.Mock;

describe('tests', () => {
  it('sample test case', async () => {
    configMock.mockReturnValue('mocked-configuration');
    const fooCheck = CustomUtility.checkIfFoo();
  });
});

I attempted to mock the customizeConfig function from CustomConfigurator.ts in CustomUtility.test.ts. I encountered an error 'configMock.mockReturnValue is not a function'.

Is there a way to properly mock an exported default function?

Answer №1

To set the value in the spec file, you can simply utilize the direct function approach. Take a look at this example:

mockConfig = () => 'mockConfig';

In this situation, using mockReturnValue is unnecessary. Appreciate it.

Answer №2

To properly test your code, make sure to add jest.mock('../MyConfig') in your testing script.

For more information on mocking modules with Jest, you can refer to the official Jest documentation: https://jestjs.io/docs/mock-functions#mocking-modules

//MyUtil.test.ts
import MyUtil from '../MyUtil';
import * as config from '../MyConfig';

jest.mock('../MyConfig')

describe('tests', () => {
  it('blah', async () => {
    config.default.mockReturnValue('mock-config');
    const foo = MyUtil.isFoo();
  });
});

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