How to mock value peer test in jest 26? - unit-testing

Question

I would like to mock value ENV_JWT_ENABLED peer test. I would like to use new value A in first test and new value B in second test. But I am getting still foo from global mock.
My current solution not working.
import { JwtAuthGuard } from './jwt-auth.guard';
jest.mock('const/env', () => ({
ENV_JWT_ENABLED: 'foo'
}));
describe('test', () => {
it('A', () => {
jest.mock('const/env', () => ({
ENV_JWT_ENABLED: 'new value A'
}));
const instance = new JwtAuthGuard(); // will print foo inside
});
it('B', () => {
jest.mock('const/env', () => ({
ENV_JWT_ENABLED: 'new value B'
}));
const instance = new JwtAuthGuard(); // will print foo inside
});
});

Answer 1

jest always prefered global vs within block, better using mockImplementationOnce with
mockImplementation provide you to mock value based on its call.
you can refer https://jestjs.io/docs/en/mock-function-api#mockfnmockimplementationoncefn chaining of mock for fn.
import { JwtAuthGuard } from './jwt-auth.guard';
jest.mock('const/env', () => {
return {
ENV_JWT_ENABLED: jest
.fn()
.mockImplementation()
.mockImplementationOnce(() => {
return 'new value A';
})
.mockImplementationOnce(() => {
return 'new value B';
})
};
});
describe('test', () => {
it('A', () => {
const instance = new JwtAuthGuard(); // will print new value A inside
});
it('B', () => {
const instance = new JwtAuthGuard(); // will print new value B inside
});
});

Answer 2

jest.mock at test level cannot affect top-level imports. jest.isolateModules or jest.resetModules can be used in conjunction with require or dynamic import to provide test-specific module mocks:
it('A', () => {
jest.isolateModules(() => {
jest.mock('const/env', () => ({
ENV_JWT_ENABLED: 'new value A'
}));
const { JwtAuthGuard } = require('./jwt-auth.guard');
const instance = new JwtAuthGuard();
});
});