openzeppelin-contracts/test/math/SafeMath.test.js

const { assertRevert } = require('../helpers/assertRevert');

const BigNumber = web3.BigNumber;
const SafeMathMock = artifacts.require('SafeMathMock');

require('chai')
  .use(require('chai-bignumber')(BigNumber))
  .should();

contract('SafeMath', () => {
  const MAX_UINT = new BigNumber(2).pow(256).minus(1);

  beforeEach(async function () {
    this.safeMath = await SafeMathMock.new();
  });

  describe('add', function () {
    it('adds correctly', async function () {
      const a = new BigNumber(5678);
      const b = new BigNumber(1234);

      const result = await this.safeMath.add(a, b);
      result.should.be.bignumber.equal(a.plus(b));
    });

    it('throws a revert error on addition overflow', async function () {
      const a = MAX_UINT;
      const b = new BigNumber(1);

      await assertRevert(this.safeMath.add(a, b));
    });
  });

  describe('sub', function () {
    it('subtracts correctly', async function () {
      const a = new BigNumber(5678);
      const b = new BigNumber(1234);

      const result = await this.safeMath.sub(a, b);
      result.should.be.bignumber.equal(a.minus(b));
    });

    it('throws a revert error if subtraction result would be negative', async function () {
      const a = new BigNumber(1234);
      const b = new BigNumber(5678);

      await assertRevert(this.safeMath.sub(a, b));
    });
  });

  describe('mul', function () {
    it('multiplies correctly', async function () {
      const a = new BigNumber(1234);
      const b = new BigNumber(5678);

      const result = await this.safeMath.mul(a, b);
      result.should.be.bignumber.equal(a.times(b));
    });

    it('handles a zero product correctly', async function () {
      const a = new BigNumber(0);
      const b = new BigNumber(5678);

      const result = await this.safeMath.mul(a, b);
      result.should.be.bignumber.equal(a.times(b));
    });

    it('throws a revert error on multiplication overflow', async function () {
      const a = MAX_UINT;
      const b = new BigNumber(2);

      await assertRevert(this.safeMath.mul(a, b));
    });
  });

  describe('div', function () {
    it('divides correctly', async function () {
      const a = new BigNumber(5678);
      const b = new BigNumber(5678);

      const result = await this.safeMath.div(a, b);
      result.should.be.bignumber.equal(a.div(b));
    });

    it('throws a revert error on zero division', async function () {
      const a = new BigNumber(5678);
      const b = new BigNumber(0);

      await assertRevert(this.safeMath.div(a, b));
    });
  });

  describe('mod', function () {
    describe('modulos correctly', async function () {
      it('when the dividend is smaller than the divisor', async function () {
        const a = new BigNumber(284);
        const b = new BigNumber(5678);

        (await this.safeMath.mod(a, b)).should.be.bignumber.equal(a.mod(b));
      });

      it('when the dividend is equal to the divisor', async function () {
        const a = new BigNumber(5678);
        const b = new BigNumber(5678);

        (await this.safeMath.mod(a, b)).should.be.bignumber.equal(a.mod(b));
      });

      it('when the dividend is larger than the divisor', async function () {
        const a = new BigNumber(7000);
        const b = new BigNumber(5678);

        (await this.safeMath.mod(a, b)).should.be.bignumber.equal(a.mod(b));
      });

      it('when the dividend is a multiple of the divisor', async function () {
        const a = new BigNumber(17034); // 17034 == 5678 * 3
        const b = new BigNumber(5678);

        (await this.safeMath.mod(a, b)).should.be.bignumber.equal(a.mod(b));
      });
    });

    it('reverts with a 0 divisor', async function () {
      const a = new BigNumber(5678);
      const b = new BigNumber(0);

      await assertRevert(this.safeMath.mod(a, b));
    });
  });
});