How to mock generic method in Java with Mockito?

Question

How can we mock the IRouteHandlerRegistry? The error is Cannot resolve method thenReturn(IHandleRoute)

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Answer 1

Even though TestRoute is a subtype of RouteDefinition, a IHandleRoute is not a subtype of IHandleRoute.

The when method from Mockito returns an object of type OngoingStubbing>. This is due to the compiler inferring the type parameter TRoute from the method

 IHandleRoute getHandlerFor(TRoute route);

to be RouteDefinition since the argument passed to getHandlerFor is declared of type RouteDefinition.

On the other hand, the thenReturn method is given an argument of type IHandleRoute whereas it expects an IHandleRoute, that is the type argument of the OngoingStubbing mentioned earlier. Hence the compiler error.

To solve this, the simplest way is probably to change the declaration type of route to be TestRoute:

TestRoute route = new TestRoute();

IRouteHandlerRegistry registry = mock(IRouteHandlerRegistry.class);
IHandleRoute handler = mock(IHandleRoute.class);

when(registry.getHandlerFor(route)).thenReturn(handler);