openzeppelin-contracts/test/helpers/increaseTime.js

import latestTime from './latestTime'

// Increases testrpc time by the passed duration in seconds
export default function increaseTime(duration) {
  const id = Date.now()

  return new Promise((resolve, reject) => {
    web3.currentProvider.sendAsync({
      jsonrpc: '2.0',
      method: 'evm_increaseTime',
      params: [duration],
      id: id,
    }, err1 => {
      if (err1) return reject(err1)

      web3.currentProvider.sendAsync({
        jsonrpc: '2.0',
        method: 'evm_mine',
        id: id+1,
      }, (err2, res) => {
        return err2 ? reject(err2) : resolve(res)
      })
    })
  })
}

/**
 * Beware that due to the need of calling two separate testrpc methods and rpc calls overhead
 * it's hard to increase time precisely to a target point so design your test to tolerate
 * small fluctuations from time to time.
 *
 * @param target time in seconds
 */
export function increaseTimeTo(target) {
  let now = latestTime();
  if (target < now) throw Error(`Cannot increase current time(${now}) to a moment in the past(${target})`);
  let diff = target - now;
  return increaseTime(diff);
}

export const duration = {
  seconds: function(val) { return val},
  minutes: function(val) { return val * this.seconds(60) },
  hours:   function(val) { return val * this.minutes(60) },
  days:    function(val) { return val * this.hours(24) },
  weeks:   function(val) { return val * this.days(7) },
  years:   function(val) { return val * this.days(365)} 
};