describe('Given that I want to allow the transfer of tokens by a third party', () => {
          it('it should return the amount I allow them to transfer', async () => {
            const amount = toWei(99);
            await this.hello_erc20.approve(holder, amount, { from: owner });
            const remaining = await this.hello_erc20.allowance(owner, holder);
            remaining.should.be.bignumber.equal(amount);
          });
        });