fix(docs): fix testing example

Author: flextremedev

docs/src/pages/guides/testing.md

@@ -36,9 +36,11 @@ const wrapper = ({ children }) => (
   </QueryClientProvider>
 );
 
-const { result } = renderHook(() => useCustomHook(), { wrapper });
+const { result, waitFor } = renderHook(() => useCustomHook(), { wrapper });
 
-expect(result.current).toEqual('Hello');
+await waitFor(() => result.current.isSuccess);
+
+expect(result.current.data).toEqual("Hello");
 ```
 
 Note that we provide a custom wrapper that builds the `QueryClient` and `QueryClientProvider`. This helps to ensure that our test is completely isolated from any other tests.