fix: .resolves and .rejects expectations (#1300)

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

@@ -1,7 +1,9 @@
 import c from 'picocolors'
+import { AssertionError } from 'chai'
 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'
@@ -55,11 +57,27 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
       return function (this: Chai.Assertion & Chai.AssertionStatic, ...args: any[]) {
         const promise = utils.flag(this, 'promise')
         const object = utils.flag(this, 'object')
+        const isNot = utils.flag(this, 'negate') as boolean
         if (promise === 'rejects') {
           utils.flag(this, 'object', () => {
             throw object
           })
         }
+        // if it got here, it's already resolved
+        // unless it tries to resolve to a function that should throw
+        // called as '.resolves[.not].toThrow()`
+        else if (promise === 'resolves' && typeof object !== 'function') {
+          if (!isNot) {
+            const message = utils.flag(this, 'message') || 'expected promise to throw an error, but it didn\'t'
+            const error = {
+              showDiff: false,
+            }
+            throw new AssertionError(message, error, utils.flag(this, 'ssfi'))
+          }
+          else {
+            return
+          }
+        }
         _super.apply(this, args)
       }
     })
@@ -426,11 +444,27 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
 
     const obj = this._obj
     const promise = utils.flag(this, 'promise')
+    const isNot = utils.flag(this, 'negate') as boolean
     let thrown: any = null
 
-    if (promise) {
+    if (promise === 'rejects') {
       thrown = obj
     }
+    // if it got here, it's already resolved
+    // unless it tries to resolve to a function that should throw
+    // called as .resolves.toThrow(Error)
+    else if (promise === 'resolves' && typeof obj !== 'function') {
+      if (!isNot) {
+        const message = utils.flag(this, 'message') || 'expected promise to throw an error, but it didn\'t'
+        const error = {
+          showDiff: false,
+        }
+        throw new AssertionError(message, error, utils.flag(this, 'ssfi'))
+      }
+      else {
+        return
+      }
+    }
     else {
       try {
         obj()
@@ -550,6 +584,10 @@ 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 '${typeof obj}'.`)
+
     const proxy: any = new Proxy(this, {
       get: (target, key, receiver) => {
         const result = Reflect.get(target, key, receiver)
@@ -564,7 +602,7 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
               return result.call(this, ...args)
             },
             (err: any) => {
-              throw new Error(`promise rejected "${err}" instead of resolving`)
+              throw new Error(`promise rejected "${toString(err)}" instead of resolving`)
             },
           )
         }
@@ -579,6 +617,10 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
     utils.flag(this, 'error', new Error('rejects'))
     const obj = utils.flag(this, 'object')
     const wrapper = typeof obj === 'function' ? obj() : obj // for jest compat
+
+    if (typeof wrapper?.then !== 'function')
+      throw new TypeError(`You must provide a Promise to expect() when using .rejects, not '${typeof wrapper}'.`)
+
     const proxy: any = new Proxy(this, {
       get: (target, key, receiver) => {
         const result = Reflect.get(target, key, receiver)
@@ -589,7 +631,7 @@ 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(value: any) {
+  try {
+    return `${value}`
+  }
+  catch (_error) {
+    return 'unknown'
+  }
+}

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

@@ -435,6 +435,47 @@ describe('async expect', () => {
   it('resolves', async () => {
     await expect((async () => 'true')()).resolves.toBe('true')
     await expect((async () => 'true')()).resolves.not.toBe('true22')
+    await expect((async () => 'true')()).resolves.not.toThrow()
+    await expect((async () => new Error('msg'))()).resolves.not.toThrow() // calls chai assertion
+    await expect((async () => new Error('msg'))()).resolves.not.toThrow(Error) // calls our assertion
+    await expect((async () => () => {
+      throw new Error('msg')
+    })()).resolves.toThrow()
+    await expect((async () => () => {
+      return new Error('msg')
+    })()).resolves.not.toThrow()
+    await expect((async () => () => {
+      return new Error('msg')
+    })()).resolves.not.toThrow(Error)
+  })
+
+  it('resolves trows chai', async () => {
+    const assertion = async () => {
+      await expect((async () => new Error('msg'))()).resolves.toThrow()
+    }
+
+    await expect(assertion).rejects.toThrowError('expected promise to throw an error, but it didn\'t')
+  })
+
+  it('resolves trows jest', async () => {
+    const assertion = async () => {
+      await expect((async () => new Error('msg'))()).resolves.toThrow(Error)
+    }
+
+    await expect(assertion).rejects.toThrowError('expected promise to throw an error, but it didn\'t')
+  })
+
+  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 () => {
@@ -443,6 +484,12 @@ describe('async expect', () => {
     })()).resolves.toBe('true')
   })
 
+  it.fails('failed to throw', async () => {
+    await expect((async () => {
+      throw new Error('err')
+    })()).resolves.not.toThrow()
+  })
+
   it('rejects', async () => {
     await expect((async () => {
       throw new Error('err')
@@ -471,6 +518,26 @@ 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)))