Async functions #

In JavaScript you very frequently work with promises and async functions. Here's how to deal with them in earl.

Successful promises #

We don't expose any helpers to work with promises that should successfully resolve. Instead, we encourage you to use async/await syntax:

function delay(n: number): Promise<void> {
  return new Promise((resolve) => {
    setTimeout(resolve, n)
  })
}

async function longTermTask(): Promise<number> {
  await delay(1000)
  return 42
}

expect(await longTermTask()).toEqual(42)

Note that if you forget await TypeScript will warn you about types mismatch because toEqual actual/expected values won't match.

Rejected promises #

For rejected promises we expose simple toBeRejected helper.

async function longTermTask(): Promise<number> {
  throw new Error('Unexpected error')
}

await expect(longTermTask()).toBeRejected('Unexpected error')

In this case we need await before expect because whole assertion becomes async. To avoid mistakes enable no-floating-promises eslint rule (it's part of TypeSTRICT).

Other than that toBeRejected works exactly the same as toThrow so you can take a look at our testing errors guide.