Two more ways to do it (see my comment on the previous answer by @Tomasz Nurkiewicz):
The first relies on the fact that the compiler simply won't let you pass in something of the wrong type:
when(a.method(any(Class.class))).thenReturn(b);
You lose the exact typing (the Class<? extends A>) but it probably works as you need it to.
The second is a lot more involved but is arguably a better solution if you really want to be sure that the argument to method() is an A or a subclass of A:
when(a.method(Matchers.argThat(new ClassOrSubclassMatcher<A>(A.class)))).thenReturn(b);
Where ClassOrSubclassMatcher is an org.hamcrest.BaseMatcher defined as:
public class ClassOrSubclassMatcher<T> extends BaseMatcher<Class<T>> {
private final Class<T> targetClass;
public ClassOrSubclassMatcher(Class<T> targetClass) {
this.targetClass = targetClass;
}
@SuppressWarnings("unchecked")
public boolean matches(Object obj) {
if (obj != null) {
if (obj instanceof Class) {
return targetClass.isAssignableFrom((Class<T>) obj);
}
}
return false;
}
public void describeTo(Description desc) {
desc.appendText("Matches a class or subclass");
}
}
Phew! I'd go with the first option until you really need to get finer control over what method() actually returns :-)