mockEndpointRequestOnce
Like mockEndpointRequest, but only the first endpoint.request is stubbed; later calls hit the real httpClient.
Returns a Vitest spy — call mockRestore() when done.
Example — first call only:
ts
mockEndpointRequestOnce(getUser, { success: { name: 'Once' } });
await getUser.request({ id: 1 }); // mocked
await getUser.request({ id: 2 }); // real HttpClient / fetch