fix: allow custom async matchers (#2707)

Author: sheremet-va

packages/expect/src/jest-extend.ts

@@ -17,9 +17,6 @@ import {
   subsetEquality,
 } from './jest-utils'
 
-const isAsyncFunction = (fn: unknown) =>
-  typeof fn === 'function' && (fn as any)[Symbol.toStringTag] === 'AsyncFunction'
-
 const getMatcherState = (assertion: Chai.AssertionStatic & Chai.Assertion, expect: Vi.ExpectStatic) => {
   const obj = assertion._obj
   const isNot = util.flag(assertion, 'negate') as boolean
@@ -56,30 +53,27 @@ class JestExtendError extends Error {
 function JestExtendPlugin(expect: Vi.ExpectStatic, matchers: MatchersObject): ChaiPlugin {
   return (c, utils) => {
     Object.entries(matchers).forEach(([expectAssertionName, expectAssertion]) => {
-      function expectSyncWrapper(this: Chai.AssertionStatic & Chai.Assertion, ...args: any[]) {
+      function expectWrapper(this: Chai.AssertionStatic & Chai.Assertion, ...args: any[]) {
         const { state, isNot, obj } = getMatcherState(this, expect)
 
         // @ts-expect-error args wanting tuple
-        const { pass, message, actual, expected } = expectAssertion.call(state, obj, ...args) as SyncExpectationResult
-
-        if ((pass && isNot) || (!pass && !isNot))
-          throw new JestExtendError(message(), actual, expected)
-      }
+        const result = expectAssertion.call(state, obj, ...args)
 
-      async function expectAsyncWrapper(this: Chai.AssertionStatic & Chai.Assertion, ...args: any[]) {
-        const { state, isNot, obj } = getMatcherState(this, expect)
+        if (result && typeof result === 'object' && result instanceof Promise) {
+          return result.then(({ pass, message, actual, expected }) => {
+            if ((pass && isNot) || (!pass && !isNot))
+              throw new JestExtendError(message(), actual, expected)
+          })
+        }
 
-        // @ts-expect-error args wanting tuple
-        const { pass, message, actual, expected } = await expectAssertion.call(state, obj, ...args) as SyncExpectationResult
+        const { pass, message, actual, expected } = result
 
         if ((pass && isNot) || (!pass && !isNot))
           throw new JestExtendError(message(), actual, expected)
       }
 
-      const expectAssertionWrapper = isAsyncFunction(expectAssertion) ? expectAsyncWrapper : expectSyncWrapper
-
-      utils.addMethod((globalThis as any)[JEST_MATCHERS_OBJECT].matchers, expectAssertionName, expectAssertionWrapper)
-      utils.addMethod(c.Assertion.prototype, expectAssertionName, expectAssertionWrapper)
+      utils.addMethod((globalThis as any)[JEST_MATCHERS_OBJECT].matchers, expectAssertionName, expectWrapper)
+      utils.addMethod(c.Assertion.prototype, expectAssertionName, expectWrapper)
 
       class CustomMatcher extends AsymmetricMatcher<[unknown, ...unknown[]]> {
         constructor(inverse = false, ...sample: [unknown, ...unknown[]]) {

test/core/test/jest-expect.test.ts

@@ -8,6 +8,9 @@ class TestError extends Error {}
 // For expect.extend
 interface CustomMatchers<R = unknown> {
   toBeDividedBy(divisor: number): R
+  toBeTestedAsync(): Promise<R>
+  toBeTestedSync(): R
+  toBeTestedPromise(): R
 }
 declare global {
   namespace Vi {
@@ -142,7 +145,7 @@ describe('jest-expect', () => {
     expect(['Bob', 'Eve']).toEqual(expect.not.arrayContaining(['Steve']))
   })
 
-  it('expect.extend', () => {
+  it('expect.extend', async () => {
     expect.extend({
       toBeDividedBy(received, divisor) {
         const pass = received % divisor === 0
@@ -161,6 +164,24 @@ describe('jest-expect', () => {
           }
         }
       },
+      async toBeTestedAsync() {
+        return {
+          pass: false,
+          message: () => 'toBeTestedAsync',
+        }
+      },
+      toBeTestedSync() {
+        return {
+          pass: false,
+          message: () => 'toBeTestedSync',
+        }
+      },
+      toBeTestedPromise() {
+        return Promise.resolve({
+          pass: false,
+          message: () => 'toBeTestedPromise',
+        })
+      },
     })
 
     expect(5).toBeDividedBy(5)
@@ -169,6 +190,11 @@ describe('jest-expect', () => {
       one: expect.toBeDividedBy(1),
       two: expect.not.toBeDividedBy(5),
     })
+    expect(() => expect(2).toBeDividedBy(5)).toThrowError()
+
+    expect(() => expect(null).toBeTestedSync()).toThrowError('toBeTestedSync')
+    await expect(async () => await expect(null).toBeTestedAsync()).rejects.toThrowError('toBeTestedAsync')
+    await expect(async () => await expect(null).toBeTestedPromise()).rejects.toThrowError('toBeTestedPromise')
   })
 
   it('object', () => {