test_can_withdraw() not working in Brownie

Question

Struggling with testing my withdraw function in a Solidity smart-contract via Brownie:

My withdrawing function is the following but in Remix it definitely works and I have tested _owner.send() and _owner.transfer() as well and both work so it has to be the test but I can not see where my error lays.

function withdrawMoney() external onlyOwner returns (bool) {
    (success, response) = _owner.call{value: address(this).balance}("");
    return success;
}

Below the brownie test that does not work. The prints and other stuff should be explained in the comments.

def test_can_withdraw():

   # ARRANGE
   buy_coffee = deploy_buycoffee()  # works fine as contract is deployed

   # ACT
   print("Before: ", buy_coffee.balance())  # Before:  0

   tx = send_money()  # works fine as tested by sending {"from": get_account(account_index=1)}

   tx.wait(1)
   print("During: ", buy_coffee.balance())  # During:  1000000000000000

   tx = buy_coffee.withdrawMoney({"from": get_account(account_index=0)})  # BROKEN!

   tx.wait(1)
   print("After: ", buy_coffee.balance())  # should be 0 but is 1000000000000000

   # ASSERT
   assert buy_coffee.balance() == 0