Support async functions as callback in pm.test

[meDavidNS]

Async functions return a promise. Currently with pm.test('description', async function () {}) will mark the test as successful and completed, even if an exception is thrown.

[meDavidNS]

The PR would still require some tests, but I would first welcome some feedback on the proposed change before tuning the PR.

[kevinswiber]

The vast majority of tests aren't going to be async functions, and we'll likely hit a small performance penalty on running all test functions through Promise resolution. Wondering if we could do something like...

try {
  const maybePromise = assert();
  if (maybePromise instanceof Promise) {
    Promise.resolve(maybePromise)
      .catch(e => markAssertionAsFailure(assertionData, e));
  }
} catch (e) {
  markAssertionAsFailure(assertionData, e);
}

onAssertionComplete(assertionData);

Alternatively, we could also check if the function's constructor name is AsyncFunction and split logic based on that without having to execute the function first.