Proxying makes use order matter with chai-exclude and chai-as-promised

[kwasimensah]

I filed the the Typescript side of this at microsoft/TypeScript#39387.

"expect.eventually" returns a Chai.PromisedAssertion which doesn't warn when using await. Which means "await expect(myPromise).eventually.to.equal(arg)" will throw UnhandledPromiseRejectionWarning if the assertion is wrong but the test will still succeed.

if expect.eventually actually returns a promise it should be safe to use with await.

[kwasimensah]

I figured out my actual issue. Both extensions do proxying on equal/equals. If chaiAsPromised isn't last, the proxy from chaiExclude drops information about the subject being a promise. Runkit at https://runkit.com/kwasimensah/5efdfbea19e9950013f020e0

const chai = require("chai")
const chaiAsPromised = require("chai-as-promised");
const chaiExclude = require("chai-exclude")

//Passes in this order
chai.use(chaiExclude);
chai.use(chaiAsPromised);

// Causes UnhandledPromiseRejectionWarning in this order
//chai.use(chaiAsPromised);
//chai.use(chaiExclude);


const expect = chai.expect;

const promiseA = new Promise((resolve) => {
    setTimeout(()=>{
    resolve(null);
    }, 1000);
});

async function  main(){
    const bug = expect(promiseA).to.eventually.equal(6)
    console.trace(bug.then);
    await bug;
}

main().catch(err=>{});

More specifically, chai-excludes's assertEqual returns undefined, which means overwritingMethodWrapper creates newAssertion which drops the then attribute that transferPromisness added to the current assertion.