diff --git a/packages/cli/src/ui/commands/extensionsCommand.test.ts b/packages/cli/src/ui/commands/extensionsCommand.test.ts
index 33ea72e30..898452a47 100644
--- a/packages/cli/src/ui/commands/extensionsCommand.test.ts
+++ b/packages/cli/src/ui/commands/extensionsCommand.test.ts
@@ -35,10 +35,18 @@ const mockGetExtensions = vi.fn();
 const mockGetLoadedExtensions = vi.fn();
 const mockInstallExtension = vi.fn();
 
-const createMockExtensionManager = () => ({
-  installExtension: mockInstallExtension,
-  getLoadedExtensions: mockGetLoadedExtensions,
-});
+const createMockExtensionManager = () => {
+  // Create a mock that passes instanceof ExtensionManager check
+  const mock = {
+    installExtension: mockInstallExtension,
+    getLoadedExtensions: mockGetLoadedExtensions,
+  };
+
+  // Set up prototype to pass instanceof check
+  Object.setPrototypeOf(mock, ExtensionManager.prototype);
+
+  return mock;
+};
 
 describe('extensionsCommand', () => {
   let mockContext: CommandContext;