jest error when trying to do unit test for functions in class in react native

Question

in accountManager.js I defined AccountManagement Class and export some functions.

class AccountManagement extends BaseManagement {

    defaultState = {};
    reduxType = 'SET_WALLET';

    constructor(state, type = 'SET_WALLET') {
        super(state, type);
    }

    ...

}

let instance = AccountManagement;

export default {

    init(state = {}) {
        instance = new AccountManagement(state);
        return instance;
    },

    get state() {
        const wallets = instance.internalState;
        return wallets
    },

   ...
}

in accountManagement.test.js

I was trying to make test code with the class.

import accountManagement from './accountManagement';


describe('accountManagement', () => {
    it('should set default state', () => {
        const manager = accountManagement.init();
        console.log(manager);
    })
})

I really do not know why manager is undefined.

If I delete the export default object and change to export default class AcccountManagement = {...}, it works.

I really cannot figure this out.