fix: only set name of mocked function if string (#12674)

CHANGELOG.md

@@ -78,6 +78,7 @@
 - `[jest-jasmine2]` Do not set `duration` to `0` for skipped tests ([#12518](https://github.com/facebook/jest/pull/12518))
 - `[jest-matcher-utils]` Pass maxWidth to `pretty-format` to avoid printing every element in arrays by default ([#12402](https://github.com/facebook/jest/pull/12402))
 - `[jest-mock]` Fix function overloads for `spyOn` to allow more correct type inference in complex object ([#12442](https://github.com/facebook/jest/pull/12442))
+- `[jest-mock]` Handle overridden `Function.name` property ([#12674](https://github.com/facebook/jest/pull/12674))
 - `[jest-reporters]` Notifications generated by the `--notify` flag are no longer persistent in GNOME Shell. ([#11733](https://github.com/facebook/jest/pull/11733))
 - `[@jest/reporters]` Move missing icon file which is needed for `NotifyReporter` class. ([#12593](https://github.com/facebook/jest/pull/12593))
 - `[jest-resolver]` Call custom resolver with core node.js modules ([#12654](https://github.com/facebook/jest/pull/12654))

packages/jest-mock/src/__tests__/index.test.ts

@@ -30,6 +30,17 @@ describe('moduleMocker', () => {
       expect(metadata.name).toBe('x');
     });
 
+    it('does not return broken name property', () => {
+      class By {
+        static name() {
+          return 'this is not a name';
+        }
+      }
+      const metadata = moduleMocker.getMetadata(By);
+      expect(typeof By.name).toBe('function');
+      expect(metadata).not.toHaveProperty('name');
+    });
+
     it('mocks constant values', () => {
       const metadata = moduleMocker.getMetadata(Symbol.for('bowties.are.cool'));
       expect(metadata.value).toEqual(Symbol.for('bowties.are.cool'));

packages/jest-mock/src/index.ts

@@ -971,8 +971,12 @@ export class ModuleMocker {
       metadata.value = component;
       return metadata;
     } else if (type === 'function') {
-      // @ts-expect-error component is a function so it has a name
-      metadata.name = component.name;
+      // @ts-expect-error component is a function so it has a name, but not
+      // necessarily a string: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/name#function_names_in_classes
+      const componentName = component.name;
+      if (typeof componentName === 'string') {
+        metadata.name = componentName;
+      }
       if (this.isMockFunction(component)) {
         metadata.mockImpl = component.getMockImplementation() as T;
       }