Mastering React Test-Driven Development

Stubbing out components built with useMemo

There is one aspect of the AppointmentForm change that is worth drawing attention to.

The AppointmentFormLoader test suite (in test/AppointmentFormLoader.test.js) has changed how it stubs out AppointmentForm. Previously, we used jest.spyOn to stub it out:

jest  .spyOn(AppointmentFormExports, 'AppointmentForm')  .mockReturnValue(null);

Unfortunately, spyOn does not work with functions that are wrapped with the connect function. connect doesn't return a function itself but instead, an object that React understands.

If that sounds a bit cryptic, think of it like this. If you were to run console.log(AppointmentForm) prior to changing it to use connect, you'd see this in your console output:

[Function: ...