Question

I’ve just started playing with Guice, and a use-case I can think of is that in a test I just want to override a single binding. I think I’d like to use the rest of the production level bindings to ensure everything is setup correctly and to avoid duplication.

So imagine I have the following Module

public class ProductionModule implements Module {     public void configure(Binder binder) {         binder.bind(InterfaceA.class).to(ConcreteA.class);         binder.bind(InterfaceB.class).to(ConcreteB.class);         binder.bind(InterfaceC.class).to(ConcreteC.class);     } } 

And in my test I only want to override InterfaceC, while keeping InterfaceA and InterfaceB in tact, so I’d want something like:

Module testModule = new Module() {     public void configure(Binder binder) {         binder.bind(InterfaceC.class).to(MockC.class);     } }; Guice.createInjector(new ProductionModule(), testModule); 

I’ve also tried the following, with no luck:

Module testModule = new ProductionModule() {     public void configure(Binder binder) {         super.configure(binder);         binder.bind(InterfaceC.class).to(MockC.class);     } }; Guice.createInjector(testModule); 

Does anyone know if it’s possible to do what I want or am I completely barking up the wrong tree??

— Follow up: It would seem I can achieve what I want if I make use of the @ImplementedBy tag on the interface and then just provide a binding in the test case, which works nicely when there is a 1-1 mapping between the interface and implementation.

Also, after discussing this with a colleague it would seem we’d head down the road of overriding an entire module and ensuring we have our modules defined correctly. This seems like it might cause a problem though where a binding is misplaced in a module and needs to be moved, thus possibly breaking a load of tests as bindings may no longer be available to be overriden.