Apartment.sol

contract Apartment is ERC20 {

    uint public balance;
    constructor() ERC20("ApartmentContract", "APRTM") {
        super._mint(_msgSender(), 100);
        console.log("Deploying a Greeter with greeting:");

    }
    
    receive() external payable {
        console.log("receive");
        balance += msg.value;
    }
}

index.ts

it("It should be possible to pay the rent and deposit it in ether in the apartment contract", async () => {
    const Apartment = await ethers.getContractFactory("Apartment");
    const apartment = await Apartment.deploy();

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

    await apartment.deployed();

    await Bob.sendTransaction({
      to: apartment.address,
      value: ethers.utils.parseEther("1")
    })

    expect(await apartment.balance()).to.equal(ethers.utils.parseEther("1"));
})