fix: toEqual throws error when comparing readonly properties

CHANGELOG.md

@@ -7,6 +7,7 @@
 
 ### Fixes
 
+- `[expect]` Handle readonly properties correctly ([#9575](https://github.com/facebook/jest/pull/9575))
 - `[jest-config]` Treat `setupFilesAfterEnv` like `setupFiles` when normalizing configs against presets ([#9495](https://github.com/facebook/jest/pull/9495))
 - `[jest-config]` Support `.mjs` config files on Windows as well ([#9558](https://github.com/facebook/jest/pull/9558))
 - `[jest-config]` Verify `rootDir` and all `roots` are directories ([#9569](https://github.com/facebook/jest/pull/9569))

packages/expect/src/__tests__/__snapshots__/matchers.test.js.snap

@@ -2113,6 +2113,20 @@ exports[`.toEqual() {pass: false} expect({"a": 5}).toEqual({"b": 6}) 1`] = `
 <d>  }</>
 `;
 
+exports[`.toEqual() {pass: false} expect({"foo": {"bar": 1}}).toEqual({"foo": {}}) 1`] = `
+<d>expect(</><r>received</><d>).</>toEqual<d>(</><g>expected</><d>) // deep equality</>
+
+<g>- Expected  - 1</>
+<r>+ Received  + 3</>
+
+<d>  Object {</>
+<g>-   "foo": Object {},</>
+<r>+   "foo": Object {</>
+<r>+     "bar": 1,</>
+<r>+   },</>
+<d>  }</>
+`;
+
 exports[`.toEqual() {pass: false} expect({"nodeName": "div", "nodeType": 1}).toEqual({"nodeName": "p", "nodeType": 1}) 1`] = `
 <d>expect(</><r>received</><d>).</>toEqual<d>(</><g>expected</><d>) // deep equality</>
 

packages/expect/src/__tests__/matchers.test.js

@@ -434,6 +434,7 @@ describe('.toEqual()', () => {
     [/abc/gsy, /abc/g],
     [{a: 1}, {a: 2}],
     [{a: 5}, {b: 6}],
+    [Object.freeze({foo: {bar: 1}}), {foo: {}}],
     ['banana', 'apple'],
     ['1\u{00A0}234,57\u{00A0}$', '1 234,57 $'], // issues/6881
     [

packages/jest-matcher-utils/src/deepCyclicCopyReplaceable.ts

@@ -59,6 +59,10 @@ function deepCyclicCopyObject<T>(object: T, cycles: WeakMap<any, any>): T {
       descriptor.value = deepCyclicCopyReplaceable(descriptor.value, cycles);
     }
 
+    if (!('set' in descriptor)) {
+      descriptor.writable = true;
+    }
+
     descriptor.configurable = true;
   });