From 2e2b17a950b21dcd5c3d15ed4a83933c474d9885 Mon Sep 17 00:00:00 2001
From: Bence Laky <blaky@users.noreply.github.com>
Date: Tue, 19 Oct 2021 08:03:03 +0200
Subject: [PATCH] fix: not to break on `expect` matcher extension overwrite
 (#11978)

---
 CHANGELOG.md                                 |  6 ++++--
 packages/expect/src/__tests__/extend.test.ts | 18 ++++++++++++++++++
 packages/expect/src/jestMatchersObject.ts    |  6 ++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 08c99d3dc8fe..a736ef807758 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,9 +4,11 @@
 
 ### Fixes
 
+- `[expect]` Make expect extension properties `configurable` ([#11978](https://github.com/facebook/jest/pull/11978))
+
 ### Chore & Maintenance
 
-- `[jest-config, jest-util]` Use `ci-info` instead of `is-ci` to detect CI environment ([11973](https://github.com/facebook/jest/pull/11973))
+- `[jest-config, jest-util]` Use `ci-info` instead of `is-ci` to detect CI environment ([#11973](https://github.com/facebook/jest/pull/11973))
 
 ### Performance
 
@@ -14,7 +16,7 @@
 
 ### Features
 
-- `[jest-config]` Add `testEnvironmentOptions.html` to apply to jsdom input ([11950](https://github.com/facebook/jest/pull/11950))
+- `[jest-config]` Add `testEnvironmentOptions.html` to apply to jsdom input ([#11950](https://github.com/facebook/jest/pull/11950))
 - `[jest-resolver]` Support default export (`.`) in `exports` field _if_ `main` is missing ([#11919](https://github.com/facebook/jest/pull/11919))
 
 ### Fixes
diff --git a/packages/expect/src/__tests__/extend.test.ts b/packages/expect/src/__tests__/extend.test.ts
index 8fdfd1d856c1..1ddd913ed07a 100644
--- a/packages/expect/src/__tests__/extend.test.ts
+++ b/packages/expect/src/__tests__/extend.test.ts
@@ -167,3 +167,21 @@ it('prints the Symbol into the error message', () => {
     }),
   ).toThrowErrorMatchingSnapshot();
 });
+
+it('allows overriding existing extension', () => {
+  jestExpect.extend({
+    toAllowOverridingExistingMatcher(_expected: unknown) {
+      return {pass: _expected === 'bar'};
+    },
+  });
+
+  jestExpect('foo').not.toAllowOverridingExistingMatcher();
+
+  jestExpect.extend({
+    toAllowOverridingExistingMatcher(_expected: unknown) {
+      return {pass: _expected === 'foo'};
+    },
+  });
+
+  jestExpect('foo').toAllowOverridingExistingMatcher();
+});
diff --git a/packages/expect/src/jestMatchersObject.ts b/packages/expect/src/jestMatchersObject.ts
index 3b15af89015e..cbfe6344a6db 100644
--- a/packages/expect/src/jestMatchersObject.ts
+++ b/packages/expect/src/jestMatchersObject.ts
@@ -99,12 +99,18 @@ export const setMatchers = <State extends MatcherState = MatcherState>(
       }
 
       Object.defineProperty(expect, key, {
+        configurable: true,
+        enumerable: true,
         value: (...sample: [unknown, ...Array<unknown>]) =>
           new CustomMatcher(false, ...sample),
+        writable: true,
       });
       Object.defineProperty(expect.not, key, {
+        configurable: true,
+        enumerable: true,
         value: (...sample: [unknown, ...Array<unknown>]) =>
           new CustomMatcher(true, ...sample),
+        writable: true,
       });
     }
   });