Each withdrawal should be calculated against new income, not total balance

index.ts

it("Each withdrawal should be calculated against new income, not total balance", async () => {
    const Apartment = await ethers.getContractFactory("Apartment");
    const apartment = await Apartment.deploy();

    [owner, Alice, Bob] = await ethers.getSigners();

    await apartment.deployed();
    await apartment.transfer(Alice.address, 20);

    //Alice balance saved for later comparison
    const aliceInitialBalanceBeforeWithdrawals = await Alice.getBalance();


    //1.
    //Bob transfers his rent
    await Bob.sendTransaction({
      to: apartment.address,
      value: ethers.utils.parseEther("1")
    });

    //Alice makes a withdrawal (20/100 * 1E) =~0.2E
    await apartment.connect(Alice).withdraw();
    //Alice account saved after withdrawal for comparison
    const aliceBalanceAfterFirstWithdrawal = await Alice.getBalance();

    //2.
    //Bob transfers his rent
    await Bob.sendTransaction({
      to: apartment.address,
      value: ethers.utils.parseEther("1")
    });
    //Alice makes withdrawal (20/10 * newIncome(1E)) =~0.2E
    await apartment.connect(Alice).withdraw();
    //Alice account after all withdrawals saved for comparison
    const aliceBalanceAfterSecondWithdrawal = await Alice.getBalance();

    expect(aliceInitialBalanceBeforeWithdrawals.lt(aliceBalanceAfterFirstWithdrawal)).to.be.true;
    expect(aliceBalanceAfterFirstWithdrawal.lt(aliceBalanceAfterSecondWithdrawal)).to.be.true;

    //apartmane balance should be following
    // 1E after Bob pays rent
    // 0.8E after Alice withdraws
    // 1.8E after Bob pays rent second time
    // 1.6 after Alice withdraws rent second time
    expect((await apartment.balance()).eq(ethers.utils.parseEther("1.6"))).to.be.true;
})