Change Promise detection code in jest-circus to support non-global Pr…

…omise implementations (#4375)

* Change Promise detection code in jest-circus to support non-global Promise implementations

To provide better interop for Promise libraries such as bluebird and Q, this changes
the part of jest-circus that detects a returned Promise from a test or hook to only
check that the value is an object with a then method on it, rather than checking that
the value is instanceof Promise. This is considered the standard way of checking for
a Promises/A+-compliant Promise. As an added bonus, this check works cross-realm.

* Update utils.js

packages/jest-circus/src/utils.js

@@ -154,8 +154,13 @@ const callAsyncFn = (
       return reject(error);
     }
 
-    // If it's a Promise, return it.
-    if (returnedValue instanceof Promise) {
+    // If it's a Promise, return it. Test for an object with a `then` function
+    // to support custom Promise implementations.
+    if (
+      typeof returnedValue === 'object' &&
+      returnedValue !== null &&
+      typeof returnedValue.then === 'function'
+    ) {
       return returnedValue.then(resolve, reject);
     }