fix(expect): preserve prototype in toMatchObject diff (#6620)

Author: hi-ogawa

packages/expect/src/jest-expect.ts

@@ -195,6 +195,7 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
     const { subset: actualSubset, stripped } = getObjectSubset(
       actual,
       expected,
+      customTesters,
     )
     if ((pass && isNot) || (!pass && !isNot)) {
       const msg = utils.getMessage(this, [

packages/expect/src/jest-utils.ts

@@ -676,7 +676,7 @@ export function getObjectKeys(object: object): Array<string | symbol> {
 export function getObjectSubset(
   object: any,
   subset: any,
-  customTesters: Array<Tester> = [],
+  customTesters: Array<Tester>,
 ): { subset: any; stripped: number } {
   let stripped = 0
 
@@ -702,13 +702,21 @@ export function getObjectSubset(
               subsetEquality,
             ])
           ) {
-          // Avoid unnecessary copy which might return Object instead of subclass.
+            // return "expected" subset to avoid showing irrelavant toMatchObject diff
             return subset
           }
 
           const trimmed: any = {}
           seenReferences.set(object, trimmed)
 
+          // preserve constructor for toMatchObject diff
+          if (typeof object.constructor === 'function' && typeof object.constructor.name === 'string') {
+            Object.defineProperty(trimmed, 'constructor', {
+              enumerable: false,
+              value: object.constructor,
+            })
+          }
+
           for (const key of getObjectKeys(object)) {
             if (hasPropertyInObject(subset, key)) {
               trimmed[key] = seenReferences.has(object[key])

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

@@ -927,12 +927,12 @@ function trim(s: string): string {
 function getError(f: () => unknown) {
   try {
     f()
-    return expect.unreachable()
   }
   catch (error) {
     const processed = processError(error)
     return [stripVTControlCharacters(processed.message), stripVTControlCharacters(trim(processed.diff))]
   }
+  return expect.unreachable()
 }
 
 it('toMatchObject error diff', () => {
@@ -1059,6 +1059,126 @@ it('toMatchObject error diff', () => {
       }",
     ]
   `)
+
+  // https://github.com/vitest-dev/vitest/issues/6543
+  class Foo {
+    constructor(public value: any) {}
+  }
+
+  class Bar {
+    constructor(public value: any) {}
+  }
+
+  expect(new Foo(0)).toMatchObject(new Bar(0))
+  expect(new Foo(0)).toMatchObject({ value: 0 })
+  expect({ value: 0 }).toMatchObject(new Bar(0))
+
+  expect(getError(() => expect(new Foo(0)).toMatchObject(new Bar(1)))).toMatchInlineSnapshot(`
+    [
+      "expected Foo{ value: +0 } to match object Bar{ value: 1 }",
+      "- Expected
+    + Received
+
+    - Bar {
+    -   "value": 1,
+    + Foo {
+    +   "value": 0,
+      }",
+    ]
+  `)
+
+  expect(getError(() => expect(new Foo(0)).toMatchObject({ value: 1 }))).toMatchInlineSnapshot(`
+    [
+      "expected Foo{ value: +0 } to match object { value: 1 }",
+      "- Expected
+    + Received
+
+    - Object {
+    -   "value": 1,
+    + Foo {
+    +   "value": 0,
+      }",
+    ]
+  `)
+
+  expect(getError(() => expect({ value: 0 }).toMatchObject(new Bar(1)))).toMatchInlineSnapshot(`
+    [
+      "expected { value: +0 } to match object Bar{ value: 1 }",
+      "- Expected
+    + Received
+
+    - Bar {
+    -   "value": 1,
+    + Object {
+    +   "value": 0,
+      }",
+    ]
+  `)
+
+  expect(getError(() =>
+    expect({
+      bad: new Foo(1),
+      good: new Foo(0),
+    }).toMatchObject({
+      bad: new Bar(2),
+      good: new Bar(0),
+    }),
+  )).toMatchInlineSnapshot(`
+    [
+      "expected { bad: Foo{ value: 1 }, …(1) } to match object { bad: Bar{ value: 2 }, …(1) }",
+      "- Expected
+    + Received
+
+      Object {
+    -   "bad": Bar {
+    -     "value": 2,
+    +   "bad": Foo {
+    +     "value": 1,
+        },
+        "good": Bar {
+          "value": 0,
+        },
+      }",
+    ]
+  `)
+
+  expect(getError(() =>
+    expect(new Foo(new Foo(1))).toMatchObject(new Bar(new Bar(0))),
+  )).toMatchInlineSnapshot(`
+    [
+      "expected Foo{ value: Foo{ value: 1 } } to match object Bar{ value: Bar{ value: +0 } }",
+      "- Expected
+    + Received
+
+    - Bar {
+    -   "value": Bar {
+    -     "value": 0,
+    + Foo {
+    +   "value": Foo {
+    +     "value": 1,
+        },
+      }",
+    ]
+  `)
+
+  expect(new Foo(new Foo(1))).toMatchObject(new Bar(new Foo(1)))
+  expect(getError(() =>
+    expect(new Foo(new Foo(1))).toMatchObject(new Bar(new Foo(2))),
+  )).toMatchInlineSnapshot(`
+    [
+      "expected Foo{ value: Foo{ value: 1 } } to match object Bar{ value: Foo{ value: 2 } }",
+      "- Expected
+    + Received
+
+    - Bar {
+    + Foo {
+        "value": Foo {
+    -     "value": 2,
+    +     "value": 1,
+        },
+      }",
+    ]
+  `)
 })
 
 it('toHaveProperty error diff', () => {