If I take a complete Backend but only use 1 of 10 methods, that relationship is better expressed as an interface with that single method. Constraining the possi

If I take a complete Backend but only use 1 of 10 methods, that relationship is better expressed as an interface with that single method. Constraining the possible behavior of that code via this kind of contract makes it easier to understand (the signature says more by permitting less) and test (the interface provides a natural mock point).