Fix .resolves and .rejects expectations

The promise helpers, .resolves and .rejects, were throwing errors when the returned object could not be serialized. Specifically, this would happen when using dynamic imports (e.g. `expect(() => import('./some_module')).resolves`). Additionally, the .resolves helper did not support a function argument even though a function was expected.

packages/vitest/src/integrations/chai/jest-expect.ts

@@ -2,6 +2,7 @@ import c from 'picocolors'
 import type { EnhancedSpy } from '../spy'
 import { isMockFunction } from '../spy'
 import { addSerializer } from '../snapshot/port/plugins'
+import { toString } from '../utils'
 import type { Constructable, Test } from '../../types'
 import { assertTypes } from '../../utils'
 import { unifiedDiff } from '../../node/diff'
@@ -550,6 +551,10 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
     utils.flag(this, 'promise', 'resolves')
     utils.flag(this, 'error', new Error('resolves'))
     const obj = utils.flag(this, 'object')
+
+    if (typeof obj?.then !== 'function')
+      throw new TypeError(`You must provide a Promise to expect() when using .resolves, not '${typeof obj}'.`)
+
     const proxy: any = new Proxy(this, {
       get: (target, key, receiver) => {
         const result = Reflect.get(target, key, receiver)
@@ -564,7 +569,7 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
               return result.call(this, ...args)
             },
             (err: any) => {
-              throw new Error(`promise rejected "${err}" instead of resolving`)
+              throw new Error(`promise rejected "${toString(err)}" instead of resolving`)
             },
           )
         }
@@ -579,6 +584,10 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
     utils.flag(this, 'error', new Error('rejects'))
     const obj = utils.flag(this, 'object')
     const wrapper = typeof obj === 'function' ? obj() : obj // for jest compat
+
+    if (typeof wrapper?.then !== 'function')
+      throw new TypeError(`You must provide a Promise to expect() when using .rejects, not '${typeof wrapper}'.`)
+
     const proxy: any = new Proxy(this, {
       get: (target, key, receiver) => {
         const result = Reflect.get(target, key, receiver)
@@ -589,7 +598,7 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
         return async (...args: any[]) => {
           return wrapper.then(
             (value: any) => {
-              throw new Error(`promise resolved "${value}" instead of rejecting`)
+              throw new Error(`promise resolved "${toString(value)}" instead of rejecting`)
             },
             (err: any) => {
               utils.flag(this, 'object', err)

packages/vitest/src/integrations/utils.ts

@@ -5,3 +5,12 @@ export function getRunningMode() {
 export function isWatchMode() {
   return getRunningMode() === 'watch'
 }
+
+export function toString(object: any) {
+  try {
+    return `${object}`
+  }
+  catch (_error) {
+    return 'unknown'
+  }
+}

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

@@ -437,6 +437,19 @@ describe('async expect', () => {
     await expect((async () => 'true')()).resolves.not.toBe('true22')
   })
 
+  it('throws an error on .resolves when the argument is not a promise', () => {
+    expect.assertions(2)
+
+    const expectedError = new TypeError('You must provide a Promise to expect() when using .resolves, not \'number\'.')
+
+    try {
+      expect(1).resolves.toEqual(2)
+    }
+    catch (error) {
+      expect(error).toEqual(expectedError)
+    }
+  })
+
   it.fails('failed to resolve', async () => {
     await expect((async () => {
       throw new Error('err')
@@ -471,6 +484,26 @@ describe('async expect', () => {
   it.fails('failed to reject', async () => {
     await expect((async () => 'test')()).rejects.toBe('test')
   })
+
+  it('throws an error on .rejects when the argument (or function result) is not a promise', () => {
+    expect.assertions(4)
+
+    const expectedError = new TypeError('You must provide a Promise to expect() when using .rejects, not \'number\'.')
+
+    try {
+      expect(1).rejects.toEqual(2)
+    }
+    catch (error) {
+      expect(error).toEqual(expectedError)
+    }
+
+    try {
+      expect(() => 1).rejects.toEqual(2)
+    }
+    catch (error) {
+      expect(error).toEqual(expectedError)
+    }
+  })
 })
 
 it('timeout', () => new Promise(resolve => setTimeout(resolve, 500)))