Alternative using Parameterize Method

IntroduceInstanceDelegator1.ts

// Alternative using Parameterize Method
export class User {
    private id: number;
    
    constructor(id: number) {
        this.id = id;
    }

    // more code...

    //!! we used Parameterize Method to pass a BankingServices instance to the method
    public updateBalance(amount: Money, bankingServices: BankingServices): void {
        bankingServices.updateBalance(this.id, amount);
    }
    
    // more code...
}

//!! In some test now we can use a test double of BankingServices to sense or separate

describe("User", () => {
    it('updates balance', () => {
        const bankingServices: jest.Mocked<BankingServices> = { updateBalance: jest.fn() };
        const userId = 1;
        const user = new User(userId);
        const amount = new Money(200);

        user.updateBalance(amount, bankingServices);

        expect(bankingServices.updateBalance).toHaveBeenCalledWith(userId, amount); // in this case sensing
    });

    // more tests...

});