не тайна, код в открытых брал. это копия какого-то мануала-примера, нашел на vc.ru вроде




pragma solidity ^0.5.0;

// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
//
// ----------------------------------------------------------------------------
contract ERC20Interface {
    function totalSupply() public view returns (uint);
    function balanceOf(address tokenOwner) public view returns (uint balance);
    function allowance(address tokenOwner, address spender) public view returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

// ----------------------------------------------------------------------------
// Safe Math Library
// ----------------------------------------------------------------------------
contract SafeMath {
    function safeAdd(uint a, uint b) public pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function safeSub(uint a, uint b) public pure returns (uint c) {
        require(b <= a); c = a - b; } function safeMul(uint a, uint b) public pure returns (uint c) { c = a * b; require(a == 0 || c / a == b); } function safeDiv(uint a, uint b) public pure returns (uint c) { require(b > 0);
        c = a / b;
    }
}


contract TESTtoken is ERC20Interface, SafeMath {
    string public name;
    string public symbol;
    uint8 public decimals; // 18 decimals is the strongly suggested default, avoid changing it
   
    uint256 public _totalSupply;
   
    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowed;
   
    /**
     * Constructor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    constructor() public {
        name = "TEST token";
        symbol = "TST";
        decimals = 18;
        _totalSupply = 1000000000000000000000000;
       
        balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }
   
    function totalSupply() public view returns (uint) {
        return _totalSupply  - balances[address(0)];
    }
   
    function balanceOf(address tokenOwner) public view returns (uint balance) {
        return balances[tokenOwner];
    }
   
    function allowance(address tokenOwner, address spender) public view returns (uint remaining) {
        return allowed[tokenOwner][spender];
    }
   
    function approve(address spender, uint tokens) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }
   
    function transfer(address to, uint tokens) public returns (bool success) {
        balances[msg.sender] = safeSub(balances[msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(msg.sender, to, tokens);
        return true;
    }
   
    function transferFrom(address from, address to, uint tokens) public returns (bool success) {
        balances[from] = safeSub(balances[from], tokens);
        allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(from, to, tokens);
        return true;
    }
}


еще есть такой, этот я на happyhodler взял. я их оба ставил, оба в тестовой сети проходили, а в обычной нет



pragma solidity ^0.4.21;

contract TESTtoken {

    uint256 totalSupply_;
    string public constant name = "TEST token";
    string public constant symbol = "TST";
    uint8 public constant decimals = 18;
    uint256 public constant initialSupply =1000000000000000000000000 ;

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    mapping (address => uint256) balances;
    mapping (address => mapping (address => uint256)) allowed;
   
    function totalSupply() public view returns (uint256){
        return totalSupply_;
    }

    function balanceOf(address _owner) public view returns (uint256){
        return balances[_owner];
    }

    function allowance(address _owner, address _spender) public view returns (uint256) {
        return allowed[_owner][_spender];
  }

    function transfer(address _to, uint256 _value) public returns (bool ) {
        require(_to != address(0));
        require(balances[msg.sender] >= _value);
        balances[msg.sender] = balances[msg.sender] - _value;
        balances[_to] = balances[_to] + _value;
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool) {
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));
        require(_value <= balances[_from]);
        require(_value <= allowed[_from][msg.sender]);
        balances[_from] = balances[_from] - _value;
        balances[_to] = balances[_to] + _value;
        allowed[_from][msg.sender] = allowed[_from][msg.sender] - _value;
        emit Transfer(_from, _to, _value);
        return true;
        }

     function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
     allowed[msg.sender][_spender] = allowed[msg.sender][_spender] + _addedValue;
     emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
     return true;
     }
 
    function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
    uint oldValue = allowed[msg.sender][_spender];
    if (_subtractedValue > oldValue) {

        allowed[msg.sender][_spender] = 0;
    }
        else {
        allowed[msg.sender][_spender] = oldValue - _subtractedValue;
    }
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
    }

    function TESTtoken() public {
        totalSupply_ = initialSupply;
        balances[msg.sender] = initialSupply;
        emit Transfer(0x0, msg.sender, initialSupply);
    }
}