@ethereum-waffle/chai/dist/esm/src/matchers/changeTokenBalance.js

A sweet set of chai matchers for your blockchain testing needs.

import { BigNumber } from 'ethers';
import { callPromise } from '../call-promise';
import { getAddressOf } from './misc/account';
export function supportChangeTokenBalance(Assertion) {
    Assertion.addMethod('changeTokenBalance', function (token, account, balanceChange, errorMargin) {
        callPromise(this);
        const isNegated = this.__flags.negate === true;
        const derivedPromise = this.callPromise.then(async () => {
            if (!('txReceipt' in this)) {
                throw new Error('The changeTokenBalance matcher must be called on a transaction');
            }
            const address = typeof account === 'string' ? account : await getAddressOf(account);
            const actualChanges = await getBalanceChange(this.txReceipt, token, address);
            return [actualChanges, address];
        }).then(([actualChange, address]) => {
            const isCurrentlyNegated = this.__flags.negate === true;
            this.__flags.negate = isNegated;
            if (errorMargin === undefined)
                errorMargin = '0';
            if (BigNumber.from(errorMargin).eq(0)) {
                this.assert(actualChange.lte(BigNumber.from(balanceChange).add(errorMargin)) &&
                    actualChange.gte(BigNumber.from(balanceChange).sub(errorMargin)), `Expected "${address}" to change balance by ${balanceChange} wei, ` +
                    `but it has changed by ${actualChange} wei`, `Expected "${address}" to not change balance by ${balanceChange} wei,`, balanceChange, actualChange);
            }
            else {
                const low = BigNumber.from(balanceChange).sub(errorMargin);
                const high = BigNumber.from(balanceChange).add(errorMargin);
                this.assert(actualChange.lte(high) &&
                    actualChange.gte(low), `Expected "${address}" balance to change within [${[low, high]}] wei, ` +
                    `but it has changed by ${actualChange} wei`, `Expected "${address}" balance to not change within [${[low, high]}] wei`, balanceChange, actualChange);
            }
            this.__flags.negate = isCurrentlyNegated;
        });
        this.then = derivedPromise.then.bind(derivedPromise);
        this.catch = derivedPromise.catch.bind(derivedPromise);
        this.callPromise = derivedPromise;
        return this;
    });
}
async function getBalanceChange(txReceipt, token, address) {
    const txBlockNumber = txReceipt.blockNumber;
    const balanceBefore = await token['balanceOf(address)'](address, { blockTag: txBlockNumber - 1 });
    const balanceAfter = await token['balanceOf(address)'](address, { blockTag: txBlockNumber });
    return balanceAfter.sub(balanceBefore);
}
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