I have a question about tx.totalFees.coins. I genuinely cannot understand what this value is supposed to represent. In my case, I want to write a test on how much gas is spent for a series of transactions.

I've provided an example at https://github.com/9oelM/ton-sandbox-totalfees-bug.git. The test setup is simple:

1. User wallet sends tx to ContractA (msg mode is 0)
2. ContractA sends tx to ContractB (msg mode is 64)

In code, it is as simple as:

it('fees test', async () => {
        const increaser = await blockchain.treasury('increaser');
        const contractBTONBalanceBefore = await contractB.getBalance();

        const increaseResult = await contractA.sendIncrease(increaser.getSender(), {
            increaseBy: 1,
            value: toNano('0.05'),
        });

        expect(increaseResult.transactions).toHaveTransaction({
            from: increaser.address,
            to: contractA.address,
            success: true,
        });
        expect(increaseResult.transactions).toHaveTransaction({
            from: contractA.address,
            to: contractB.address,
            success: true,
        });

        printTransactionFees(increaseResult.transactions);

        const allFees = increaseResult.transactions.reduce((acc, tx) => {
            return acc + tx.totalFees.coins;
        }, 0n)
        
        const contractBTONBalanceAfter = await contractB.getBalance();
        console.log('contractB TON inflow', contractBTONBalanceAfter - contractBTONBalanceBefore);

        const lastTx = flattenTransaction(increaseResult.transactions[increaseResult.transactions.length - 1]);
        expect(lastTx.value! - lastTx.totalFees!).toBe(
            toNano('0.05') - allFees
        );
    });

printTransactionFees(increaseResult.transactions); prints:

But I couldn't wrap my head around these numbers. I thought totalFees is supposed to be the sum of all total fees for a tx. In other words, $valueIn - valueOut = totalFees$. But this simply isn't the case:

1. For index = 0, valueIn = 0.05 TON (we started with 0.05 TON) and valueOut = 0.0496 TON. valueIn - valueOut = 0.0004. But totalFees = 0.001613???
2. Same for index = 1. valueIn = 0.0496 TON and valueOut = 0.046978 TON. valueIn - valueOut = 0.002622. But totalFees = 0.002296???

If totalFees were correctly calculated as total gas for the tx, toNano('0.05') - allFees would simply match the TON balance transferred to a contract, which is contractBTONBalanceAfter - contractBTONBalanceBefore. But this is not the case. In fact, lastTx.value - lastTx.totalFees == contractBTONBalanceAfter - contractBTONBalanceBefore != toNano('0.05') - allFees:

• lastTx.value! - lastTx.totalFees! = 45904800n
• contractBTONBalanceAfter - contractBTONBalanceBefore = 45904800n
• toNano('0.05') - allFees = 45020139n

cc @krigga