Assertion helper for async/promise methods that should fail

rejects.js

Assert.rejects = async function rejects (blockOrPromise, error, message)  {
    return new Promise((resolve,reject) => {
        if (typeof blockOrPromise === 'function') {
            blockOrPromise = blockOrPromise()
        }
        blockOrPromise.then(x => {
            reject(Error('Should fail, not return ' + x))
        }).catch(async err => {
            if (typeof error === 'function') {
                err = (await error(err)) || err
            }
            else if (error instanceof RegExp) {
                Assert.ok(error.test(err.message), message || err.stack)
            }
            else if (typeof error === 'string') {
                Assert.strictEqual(err.message, error, message || err.stack)
            }
            else {
                Assert.equal(err, error, message || err.stack)
            }
            resolve(err)
        })
        .catch(reject)
    })
}