为什么Jest错误没有try / catch块进行异步测试

Question

I'm learning Jest and when I run this first example I get an error when running the test. If I wrap it in a try/catch block it works fine. The docs show examples without try/catch. Why is the first example error?

ERRORS

  test('controller type error is correct', async () => {
    expect(await pipe('string', podchain)).toThrow('VALIDATE PROPS: podchain must be an object.')
  })

DOES NOT ERROR

  test('controller type error is correct', async () => {
    try {
      expect(await pipe('string', podchain)).toThrow('VALIDATE PROPS: podchain must be an object.')
    } catch (e) {
      console.log(e.message)
    }
  })

Answer 1

The .toThrow() expectation is supposed to work on a function, and await pipe('string', podchain)) isn't a function that throws. In a normal async function, try-catch blocks are re-written to be .catch() terms on the end of promises, but in jest that re-write doesn't work.

I suggest using the Jest .rejects helper:

await expect(pipe('string', podchain)).rejects.toThrow();

See https://jestjs.io/docs/en/expect#rejects