Example function selector as a member of a function. Should revert if ERC20 transfer is passed.

QueryContract.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.4.22 <0.9.0;


contract QueryContract {

    event Selector(bytes4);

    function query(bytes memory data, function(address,uint) external test) public {
        emit Selector(test.selector);
        if(test.selector == 0xa9059cbb)
            revert();
    }
}


contract QueryUser {
    QueryContract public query;

constructor (){
    query = new QueryContract();
}
    function callQueryTransfer() public {
        query.query("This should revert", this.transfer);
    }



    function callQueryNotTransfer() public {
        query.query("This is ok", this.notTransfer);
    }
   
    function transfer(address dest, uint256 amount) external {
        //
    }

    function notTransfer(address dest, uint256 amount) external{
        //
    }

}