How to mock global variable in Jest test?

Question

In my Jest test case, I want to mock one global variable, but I am getting Cannot assign to '' because it is an import. . How to fix that?

I want to cover a scenario where I do have valid token then do something.

Tried this but no luck:

• jest.mock('jwtToken', () => () => ({ jwtToken: 'abc' }));

Service.ts

export let token: string;

@Injectable()
    export class MyService {
      constructor(
      ) {
        token = null;
      }
    
    
      /**
       * Checks token expiration to avoid N calls to generate token.
       * @returns token status
       */
      public async myFunction() {
        try {
          if (token) {
          // Do something
          }
        } catch (error) {
          throw error;
        }
      }
    }

Service.spec.ts

import { MyService, token } from './authz.service';

describe('MyService', () => {
  let myService: MyService;

  beforeEach(() => {
    jest.resetAllMocks();
    jest.resetModules();


    myService = new MyService();
  });

  describe('myFunction()', () => {

    it('My test case', async () => {
     
      token = 123; // Cannot assign to 'jwtToken' because it is an import.

      const output = await myService.myFunction();
      expect(output).toEqual(true);
    });
  });
});