Jest: async behavior incorrect

[Himself65]

🐛 Bug Report

Error: expect(received).toThrow()

Received function did not throw

To Reproduce

async function foo (a, b) {
    if (a == null || b == null) {
        throw new TypeError()
    }
    return new Promise((resolve, reject) => {
        // do something
        resolve('success')
    })
}

describe('something', () => {
    it('should throw error', () => {
        expect(() => foo()).toThrow()
    })
})

Expected behavior

This test should pass

Run npx envinfo --preset jest

  System:
    OS: Windows 10
    CPU: (4) x64 Intel(R) Core(TM) i7-7660U CPU @ 2.50GHz
  Binaries:
    Node: 11.12.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.15.2 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
    npm: 6.7.0 - C:\Program Files\nodejs\npm.CMD

[scotthovestadt]

When you throw an Error in an async function, the error is automatically caught and used to reject the Promise. Promise rejection is not the same thing as an Error being thrown, although I understand why it's confusing since async methods can be caught with try/catch.

See:
https://jestjs.io/docs/en/tutorial-async#rejects

[Himself65]

@scotthovestadt

thanks for helping