fix: correct isPromise implementation

packages/expect/src/index.ts

@@ -10,6 +10,7 @@
 
 import {equals, iterableEquality, subsetEquality} from '@jest/expect-utils';
 import * as matcherUtils from 'jest-matcher-utils';
+import {isPromise} from 'jest-util';
 import {
  any,
  anything,
@@ -69,12 +70,6 @@ export class JestAssertionError extends Error {
  matcherResult?: Omit<SyncExpectationResult, 'message'> & {message: string};
 }
 
-// eslint-disable-next-line @typescript-eslint/no-unnecessary-type-constraint
-const isPromise = <T extends any>(obj: any): obj is PromiseLike<T> =>
- !!obj &&
- (typeof obj === 'object' || typeof obj === 'function') &&
- typeof obj.then === 'function';
-
 const createToThrowErrorMatchingSnapshotMatcher = function (
  matcher: RawMatcherFn,
 ) {

packages/jest-circus/src/utils.ts

@@ -13,7 +13,12 @@ import slash = require('slash');
 import StackUtils = require('stack-utils');
 import type {AssertionResult, Status} from '@jest/test-result';
 import type {Circus, Global} from '@jest/types';
-import {ErrorWithStack, convertDescriptorToString, formatTime} from 'jest-util';
+import {
+ ErrorWithStack,
+ convertDescriptorToString,
+ formatTime,
+ isPromise,
+} from 'jest-util';
 import {format as prettyFormat} from 'pretty-format';
 import {ROOT_DESCRIBE_BLOCK_NAME, getState} from './state';
 
@@ -266,13 +271,7 @@ export const callAsyncCircusFn = (
  }
  }
 
- // 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'
- ) {
+ if (isPromise(returnedValue)) {
  returnedValue.then(() => resolve(), reject);
  return;
  }

packages/jest-jasmine2/src/jasmineAsyncInstall.ts

@@ -14,15 +14,12 @@ import co from 'co';
 import isGeneratorFn from 'is-generator-fn';
 import pLimit = require('p-limit');
 import type {Config, Global} from '@jest/types';
+import {isPromise} from 'jest-util';
 import isError from './isError';
 import type Spec from './jasmine/Spec';
 import type {DoneFn, QueueableFn} from './queueRunner';
 import type {Jasmine} from './types';
 
-function isPromise(obj: any): obj is PromiseLike<unknown> {
- return obj && typeof obj.then === 'function';
-}
-
 // eslint-disable-next-line @typescript-eslint/no-empty-function
 const doneFnNoop = () => {};
 

packages/jest-util/src/__tests__/isPromise.test.ts

@@ -23,3 +23,12 @@ test('a resolved Promise', () => {
 test('a rejected Promise', () => {
  expect(isPromise(Promise.reject().catch(() => {}))).toBe(true);
 });
+
+test('a thenable', () => {
+ expect(isPromise({then: () => 'hello'})).toBe(true);
+});
+
+test('an async function', () => {
+ async function asyncFn() {}
+ expect(isPromise(asyncFn())).toBe(true);
+});

packages/jest-util/src/isPromise.ts

@@ -5,10 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-// capture globalThis.Promise before it may potentially be overwritten
-const Promise = globalThis.Promise;
-
-// see ES2015 spec 25.4.4.5, https://stackoverflow.com/a/38339199
-const isPromise = (candidate: unknown): candidate is Promise<unknown> =>
- Promise.resolve(candidate) === candidate;
-export default isPromise;
+export default function isPromise<T = unknown>(
+ candidate: unknown,
+): candidate is PromiseLike<T> {
+ return (
+ candidate != null &&
+ (typeof candidate === 'object' || typeof candidate === 'function') &&
+ typeof (candidate as any).then === 'function'
+ );
+}

packages/jest-worker/src/workers/processChild.ts

@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import {isPromise} from 'jest-util';
 import {
  CHILD_MESSAGE_CALL,
  CHILD_MESSAGE_END,
@@ -158,11 +159,6 @@ function execMethod(method: string, args: Array<unknown>): void {
  execFunction(main.setup, main, setupArgs, execHelper, reportInitializeError);
 }
 
-const isPromise = (obj: any): obj is PromiseLike<unknown> =>
- !!obj &&
- (typeof obj === 'object' || typeof obj === 'function') &&
- typeof obj.then === 'function';
-
 function execFunction(
  fn: UnknownFunction,
  ctx: unknown,

packages/jest-worker/src/workers/threadChild.ts

@@ -6,6 +6,7 @@
  */
 
 import {isMainThread, parentPort} from 'worker_threads';
+import {isPromise} from 'jest-util';
 import {
  CHILD_MESSAGE_CALL,
  CHILD_MESSAGE_END,
@@ -160,11 +161,6 @@ function execMethod(method: string, args: Array<unknown>): void {
  execFunction(main.setup, main, setupArgs, execHelper, reportInitializeError);
 }
 
-const isPromise = (obj: any): obj is PromiseLike<unknown> =>
- !!obj &&
- (typeof obj === 'object' || typeof obj === 'function') &&
- typeof obj.then === 'function';
-
 function execFunction(
  fn: UnknownFunction,
  ctx: unknown,