confusing contract's balance with externalContract's balance

Question

The total code is here in my gist https://gist.github.com/supersuperrookie/0cd4584c691c88af9aaa43d67fb730cd

I created a smart contract which has the below function,

function execute() public checkExternalStatus checkDeadline(false) {
    uint256 balanceAmount = address(this).balance;
    require(balanceAmount > threshold, "threshold is not reached");
    (bool sent, ) = address(exampleExternalContract).call{
    value: balanceAmount
    }(abi.encodeWithSignature("complete()"));
require(sent, "exampleExternalContract.complete failed");
}

and when I test this method like this, i do not know why stakerContractbalance is 0 (★)

it('external contract sucessfully completed', async() => {
      const amount = ethers.utils.parseEther('1.1');
      await stakerContract.connect(addr1).stake({
        value :amount,
      });
      await stakerContract.connect(addr1).execute();

      const competed = await exampleExternalContract.completed();
      expect(competed).to.equal(true);

      const externalBalance = await ethers.provider.getBalance(exampleExternalContract.address);
      expect(externalBalance).to.equal(amount);

      const stakerContractbalance = await ethers.provider.getBalance(stakerContract.address);
   --(★)confuing witch this line(why stakerContractbalance is 0?)           
  expect(stakerContractbalance).to.equal(0); 

});