Lesson 13: unstakeTokens function update

[haraslub]

Hello,
I am trying to extend the function unstakeTokens() by defining the amount of a token to be unstaked from the farm. Unfortunately, the test of the function always fails. I get:
brownie.exceptions.VirtualMachineError: revert: ERC20: transfer amount exceeds balance
Could anyone help me to solve this, please?

The unstake function is:

function unstakeTokens(address _token, uint256 _amount) public {
        uint256 balance = stakingBalance[_token][msg.sender];
        require(balance > 0, "Staking balance cannot be zero.");
        require(stakingBalance[_token][msg.sender] <= _amount, "Do not have this amount of token staked.");
        IERC20(_token).transferFrom(address(this), msg.sender, _amount);
        stakingBalance[_token][msg.sender] = stakingBalance[_token][msg.sender] - _amount;
        if (stakingBalance[_token][msg.sender] == 0) {
            uniqueTokenStaked[msg.sender] = uniqueTokenStaked[msg.sender] - 1;
            removeStaker(msg.sender);
        }
    }

Testing:

# amount_staked defined in conftest.py as 1 ether

def test_unstake_tokens(amount_staked):
    # Arrange
    if network.show_active() not in LOCAL_BLOCKCHAIN_ENVIRONMENTS:
        pytest.skip("Only for local testing!")
    account = get_account()
    token_farm, dapp_token = test_stake_tokens(amount_staked)
    # Act
    tx_unstake = token_farm.unstakeTokens(dapp_token.address, amount_staked, {"from": account})
    tx_unstake.wait(1)
    # Assert
    assert token_farm.stakingBalance(dapp_token.address, account.address) == 0
    assert token_farm.stakers(0) != account.address

def test_stake_tokens(amount_staked):
    # Arrange
    if network.show_active() not in LOCAL_BLOCKCHAIN_ENVIRONMENTS:
        pytest.skip("Only for local testing!")
    account = get_account()
    token_farm, dapp_token = deploy_token_farm_and_dapp_token()
    # Act
    # Approve to the token farm to stake our tokens 
    tx_approve = dapp_token.approve(token_farm.address, amount_staked, {"from": account})
    tx_approve.wait(1)
    # Stake our token
    tx_stake = token_farm.stakeTokens(dapp_token.address, amount_staked, {"from": account})
    tx_stake.wait(1)
    # Assert
    # 1) current staking balance must equal to amount staked
    assert token_farm.stakingBalance(dapp_token.address, account.address) == amount_staked
    # 2) test, if only one token has been staked
    assert token_farm.uniqueTokenStaked(account.address) == 1
    # 3) the first staker is us
    assert token_farm.stakers(0) == account.address
    # return token farm and dapp token to be able to use it in further testing
    return token_farm, dapp_token

Thank you very much in advance.

[haraslub]

Solved, the following line:
IERC20(_token).transferFrom(address(this), msg.sender, _amount);
replaced by:
IERC20(_token).transfer(msg.sender, _amount);

[cromewar]

Hello @haraslub sorry for the delay answering (rough day) I'm glad you managed to solve your problem, please feel free to make any other questions.