I’m not sure I manage to follow the author correctly, but to me it seems that by “mock” they strictly refer to external mocking libraries, in the sense of JS’s

I’m not sure I manage to follow the author correctly, but to me it seems that by “mock” they strictly refer to external mocking libraries, in the sense of JS’s `testdouble` [1] or Java’s `Mockito` [2]. The static fake object as returned by `LoginClient.createNull().getUserInfo(...)` appears to be a “Nullable” for them. [1] https://www.npmjs.com/package/testdouble https://www.npmjs.com/package/testdouble [2] https://site.mockito.org/ https://site.mockito.org/