feat: improve deep equality check failing message for toBe (#1383)

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

@@ -7,7 +7,7 @@ import type { Constructable, Test } from '../../types'
 import { assertTypes } from '../../utils'
 import { unifiedDiff } from '../../node/diff'
 import type { ChaiPlugin, MatcherState } from '../../types/chai'
-import { arrayBufferEquality, iterableEquality, equals as jestEquals, sparseArrayEquality, subsetEquality, typeEquality } from './jest-utils'
+import { arrayBufferEquality, generateToBeMessage, iterableEquality, equals as jestEquals, sparseArrayEquality, subsetEquality, typeEquality } from './jest-utils'
 import type { AsymmetricMatcher } from './jest-asymmetric-matchers'
 import { stringify } from './jest-matcher-utils'
 
@@ -129,9 +129,41 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
   })
   def('toBe', function (expected) {
     const actual = this._obj
+    const pass = Object.is(actual, expected)
+
+    let deepEqualityName = ''
+
+    if (!pass) {
+      const toStrictEqualPass = jestEquals(
+        actual,
+        expected,
+        [
+          iterableEquality,
+          typeEquality,
+          sparseArrayEquality,
+          arrayBufferEquality,
+        ],
+        true,
+      )
+
+      if (toStrictEqualPass) {
+        deepEqualityName = 'toStrictEqual'
+      }
+      else {
+        const toEqualPass = jestEquals(
+          actual,
+          expected,
+          [iterableEquality],
+        )
+
+        if (toEqualPass)
+          deepEqualityName = 'toEqual'
+      }
+    }
+
     return this.assert(
-      Object.is(actual, expected),
-      'expected #{this} to be #{exp} // Object.is equality',
+      pass,
+      generateToBeMessage(deepEqualityName),
       'expected #{this} not to be #{exp} // Object.is equality',
       expected,
       actual,

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

@@ -508,3 +508,16 @@ export const sparseArrayEquality = (
     equals(a, b, [iterableEquality, typeEquality], true) && equals(aKeys, bKeys)
   )
 }
+
+export const generateToBeMessage = (
+  deepEqualityName: string,
+  expected = '#{this}',
+  actual = '#{exp}',
+) => {
+  const toBeMessage = `expected ${expected} to be ${actual} // Object.is equality`
+
+  if (['toStrictEqual', 'toEqual'].includes(deepEqualityName))
+    return `${toBeMessage}\n\nIf it should pass with deep equality, replace "toBe" with "${deepEqualityName}"\n\nExpected: ${expected}\nReceived: serializes to the same string\n`
+
+  return toBeMessage
+}

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

@@ -1,5 +1,7 @@
 /* eslint-disable no-sparse-arrays */
+import { AssertionError } from 'assert'
 import { describe, expect, it, vi } from 'vitest'
+import { generateToBeMessage } from 'vitest/src/integrations/chai/jest-utils'
 
 class TestError extends Error {}
 
@@ -548,6 +550,52 @@ describe('async expect', () => {
       expect(error).toEqual(expectedError)
     }
   })
+
+  it('reminds users to use deep equality checks if they are comparing objects', () => {
+    const generatedToBeMessage = (
+      deepEqualityName: string,
+      expected: string,
+      actual: string,
+    ) => new AssertionError({
+      message: generateToBeMessage(deepEqualityName, expected, actual),
+    })
+
+    const actual = { key: 'value' }
+    class FakeClass {}
+
+    const toStrictEqualError1 = generatedToBeMessage('toStrictEqual', '{ key: \'value\' }', '{ key: \'value\' }')
+    try {
+      expect(actual).toBe({ ...actual })
+    }
+    catch (error) {
+      expect(error).toEqual(toStrictEqualError1)
+    }
+
+    const toStrictEqualError2 = generatedToBeMessage('toStrictEqual', 'FakeClass{}', 'FakeClass{}')
+    try {
+      expect(new FakeClass()).toBe(new FakeClass())
+    }
+    catch (error) {
+      expect(error).toEqual(toStrictEqualError2)
+    }
+
+    const toEqualError1 = generatedToBeMessage('toEqual', '{}', 'FakeClass{}')
+    try {
+      expect({}).toBe(new FakeClass())
+    }
+    catch (error) {
+      expect(error).toEqual(toEqualError1)
+      // expect(error).toEqual('1234')
+    }
+
+    const toEqualError2 = generatedToBeMessage('toEqual', 'FakeClass{}', '{}')
+    try {
+      expect(new FakeClass()).toBe({})
+    }
+    catch (error) {
+      expect(error).toEqual(toEqualError2)
+    }
+  })
 })
 
 it('timeout', () => new Promise(resolve => setTimeout(resolve, 500)))