fix: not to break on expect matcher extension overwrite (#11978)

jestjs · Oct 19, 2021 · 2e2b17a · 2e2b17a
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -4,17 +4,19 @@
 
 ### 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
 
 ## 27.3.0
 
 ### 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
@@ -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
@@ -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,
       });
     }
   });