a mock clock for tests involving timing
npm install clock-mockA mock clock for tests involving timing.
Don't just use setTimeout() and hope that the timings work out. This
makes tests take forever and be non-deterministic and flaky.
Instead, mock the clock, and explicitly advance it so you can test timing
issues precisely and deterministically.
``js
import { Clock } from 'clock-mock'
// this also works:
// const { Clock } = require('clock-mock')
import t from 'tap' // or whatever you use
// the module you wrote that does timing stuff
import { myModuleThatDoesStuffWithTime } from '../index.js'
t.test('test timeouts precisely', t => {
const c = new Clock()
c.enter()
myModuleThatDoesStuffWithTime.scheduleThing('foo', 100)
c.advance(99)
t.equal(myModuleThatDoesStuffWithTime.thingRan('foo'), false)
c.advance(1) // the timeout fired!
t.equal(myModuleThatDoesStuffWithTime.thingRan('foo'), true)
c.exit()
t.end()
})
`
Patches:
- Date class
- setTimeout
- setInterval
- setImmediate
- clearTimeout
- clearInterval
- performance.now()
- process.hrtime
- process.hrtime.bigint
- const c = new Clock()
Returns a new Clock instance
- c.advance(n)
Advance the clock by n ms. Use floats for smaller increments of
time.
- c.flow(n, step = 5) => Promise
Advance the clock in steps, awaiting a Promise at each step,
so that actual asynchronous events can occur, as well as
timers.
- c.travel(time)
Set the clock to a specific time. Will fire timers that you zoom past.
- c.enter()
Mocks all the things in the global space.
Returns exit function, for ease of doing t.teardown(c.enter()).
- c.exit()
Puts all the mocked globals back to their prior state.
- c.setTimeout(fn, n = 1)
Schedule a function to be run when the clock has advanced n ms beyond
the current point.
Only ms granularity.
- c.setInterval(fn, n = 1)
Schedule a function to be run when the clock advances each multiple of
n past the current point.
If multiple steps are advanced at once, for example doing
c.setInterval(fn, 1) ; c.advance(1000), then it will only call the
function once. This allows you to simulate clock jitter.
Only ms granularity.
- c.setImmediate(fn)
Schedule a function to be run the next time the clock advances
by any amount.
- c.clearTimeout(timer)
Clear a timeout created by the clock.
- c.clearInterval(interval)
Clear an interval created by the clock.
- c.now()
Returns the current ms time on the clock.
- c.hrtime()
Mock of process.hrtime(), returning [seconds, nanoseconds] on the
clock.
- c.hrtimeBigint()
Mock of process.hrtime.bigint()`, returning BigInt representation of
current nanosecond time.