Die Gaskosten summieren sich im einfachen Transaktionsvertrag nicht

Ich habe einen einfachen Vertrag, der hilft, eine Zahlung auf ein anderes Konto vorzunehmen. Nehmen wir an, ich beginne den Vertrag mit Wert V, Vertragsgaskosten Gund Wert, der in das andere Konto umgerechnet wird X. Ich gehe davon aus, dass folgendes zutreffen wird:

V = G + X.

Es ist jedoch nicht.

Nach einem einfachen truffle initSchritt arbeite ich mit dem folgenden Vertrag.

Pay.sol

pragma solidity ^0.4.17;

/// @title Pay - Facilitates payments.
contract Pay {
    event Payment(
        address _from,
        address _to,
        uint amount
    );

    /// @dev Makes a payment.
    /// @param _to Address to pay to.
    function pay(address _to) public payable {
        require(msg.value > 0);
        // Does this transfer the right amount of ether (msg.value measured in wei)?
        _to.transfer(msg.value);
        Payment(msg.sender, _to, msg.value);
    }
}

Und die folgende Testdatei.

pay.js

var Pay = artifacts.require("./Pay.sol");

contract('Pay', function(accounts) {
    it("should put money in the first account", function() {
        return Pay.deployed().then(function(instance) {
            pay = instance;
            return web3.eth.getBalance(accounts[1]);
        }).then(function(balance){
            startingBalance = balance.toNumber();
            gasPrice = 200000;
            payAmount = 2500000;
            return pay.pay(accounts[1], {from: accounts[0], value: payAmount, gasPrice: gasPrice });
        }).then(function() {
            return pay.pay.estimateGas(accounts[1], {from: accounts[0], value: payAmount });
        }).then(function(gasCost) {
            gasSpent = gasCost * gasPrice;
            console.log(gasCost);
            console.log(gasPrice);
            console.log(gasSpent);
            return web3.eth.getBalance(accounts[1]);
        }).then(function(balance) {
            endingBalance = balance.toNumber();
            assert.equal(endingBalance - startingBalance, payAmount);
        })
    });
});

Die Ausgabe ist die folgende:

  Contract: Pay
32001
200000
6400200000
    1) should put money in the first account

    Events emitted during test:
    ---------------------------

    Payment(_from: 0x627306090abab3a6e1400e9345bc60c78a8bef57, _to: 0xf17f52151ebef6c7334fad080c5704d77216b732, amount: 2500000)

    ---------------------------


  0 passing (476ms)
  1 failing

  1) Contract: Pay should put money in the first account:
     AssertionError: expected 2506752 to equal 2500000
      at test/pay.js:23:20
      at <anonymous>
      at process._tickCallback (internal/process/next_tick.js:118:7)

Insbesondere, wie Sie der Ausgabe entnehmen können:

V-X=-6752(kann es auch negativ sein?)G=6400200000

UPDATE : Richtige Antwort als Referenz.

pay.js

var Pay = artifacts.require("./Pay.sol");

contract('Pay', function(accounts) {
    it("should put money in the first account", function() {
        return Pay.deployed().then(function(instance) {
            pay = instance;
            return web3.eth.getBalance(accounts[1]);
        }).then(function(balance){
            startingBalance = balance;
            gasPrice = 200000;
            payAmount = 2500000;
            return pay.pay(accounts[1], {from: accounts[0], value: payAmount, gasPrice: gasPrice });
        }).then(function(result) {
            gasUsed = result.receipt.gasUsed;
            return pay.pay.estimateGas(accounts[1], {from: accounts[0], value: payAmount });
        }).then(function(gasCost) {
            gasSpent = gasCost * gasPrice;
            return web3.eth.getBalance(accounts[1]);
        }).then(function(balance) {
            endingBalance = balance;
            assert.equal(endingBalance.sub(startingBalance).toNumber(), payAmount);
        })
    });

    it("should pay gas costs from the second account", function() {
        return Pay.deployed().then(function(instance) {
            pay = instance;
            return web3.eth.getBalance(accounts[0]);
        }).then(function(balance){
            startingBalance = balance;
            gasPrice = 200000;
            payAmount = 2500000;
            return pay.pay(accounts[1], {from: accounts[0], value: payAmount, gasPrice: gasPrice });
        }).then(function(result) {
            gasUsed = result.receipt.gasUsed;
            return pay.pay.estimateGas(accounts[1], {from: accounts[0], value: payAmount });
        }).then(function(gasCost) {
            gasSpent = gasCost * gasPrice;
            return web3.eth.getBalance(accounts[0]);
        }).then(function(balance) {
            endingBalance = balance;
            assert.equal(startingBalance.sub(endingBalance).toNumber(), payAmount + gasSpent);
        })
    });
});