Instead of duplicating many interfaces with mock interfaces, and reimplementing mocks multiple times in several files to meet those interfaces, it is preferable to implement a versatile mock once, to meet the real interface, and then import it where used.
I'm not sure I'm understanding the idea correctly.
The point is that we most often have to have different mock implementations for different test cases
https://github.com/penumbra-zone/web/blob/main/packages/router/src/grpc/test-utils.ts
Instead of duplicating many interfaces with mock interfaces, and reimplementing mocks multiple times in several files to meet those interfaces, it is preferable to implement a versatile mock once, to meet the real interface, and then import it where used.