fix: add unit tests

scripts/create-package/utils.test.ts

@@ -87,9 +87,10 @@ describe('create-package/utils', () => {
         nodeVersions: '>=18.0.0',
       };
 
-      (fs.promises.stat as jest.Mock).mockResolvedValueOnce({
-        isDirectory: () => false,
-      });
+      const mockError = new Error('Not found') as NodeJS.ErrnoException;
+      mockError.code = 'ENOENT';
+
+      jest.spyOn(fs.promises, 'stat').mockRejectedValue(mockError);
 
       (fsUtils.readAllFiles as jest.Mock).mockResolvedValueOnce({
         'src/index.ts': 'export default 42;',
@@ -181,5 +182,34 @@ describe('create-package/utils', () => {
       expect(fs.promises.mkdir).not.toHaveBeenCalled();
       expect(fs.promises.writeFile).not.toHaveBeenCalled();
     });
+
+    it('throws if fs.stat fails with an error other than ENOENT', async () => {
+      const mockError = new Error('Permission denied') as NodeJS.ErrnoException;
+      mockError.code = 'EACCES';
+
+      jest.spyOn(fs.promises, 'stat').mockRejectedValue(mockError);
+
+      const packageData: PackageData = {
+        name: '@metamask/foo',
+        description: 'A foo package.',
+        directoryName: 'foo',
+        nodeVersions: '20.0.0',
+        currentYear: '2023',
+      };
+
+      const monorepoFileData = {
+        tsConfig: {
+          references: [{ path: './packages/bar' }],
+        },
+        tsConfigBuild: {
+          references: [{ path: './packages/bar' }],
+        },
+        nodeVersions: '20.0.0',
+      };
+
+      await expect(
+        finalizeAndWriteData(packageData, monorepoFileData),
+      ).rejects.toThrow('Permission denied');
+    });
   });
 });