java - 如何使用 Mockito 模拟 Java 中的泛型方法？

Question

我们如何模拟 IRouteHandlerRegistry ？错误是 Cannot resolve method thenReturn(IHandleRoute<TestRoute>)

public interface RouteDefinition { }

public class TestRoute implements RouteDefinition { }

public interface IHandleRoute<TRoute extends RouteDefinition> {
    Route getHandlerFor(TRoute route);
}

public interface IRouteHandlerRegistry {
    <TRoute extends RouteDefinition> IHandleRoute<TRoute> getHandlerFor(TRoute route);
}

@Test
@SuppressWarnings("unchecked")
public void test() {
    // in my test
    RouteDefinition route = new TestRoute(); // TestRoute implements RouteDefinition
    IRouteHandlerRegistry registry = mock(IRouteHandlerRegistry.class);
    IHandleRoute<TestRoute> handler = mock(IHandleRoute.class);

    // Error: Cannot resolve method 'thenReturn(IHandleRoute<TestRoute>)'
    when(registry.getHandlerFor(route)).thenReturn(handler);
}

Answer 1

尽管TestRoute是 RouteDefinition 的子类型, 一个 IHandleRoute<TestRoute> 不是 IHandleRoute<RouteDefinition> 的子类型.

when Mockito 的方法返回类型为 OngoingStubbing<IHandleRoute<RouteDefinition>> 的对象.这是由于编译器推断类型参数 TRoute从方法

<TRoute extends RouteDefinition> IHandleRoute<TRoute> getHandlerFor(TRoute route);

成为 RouteDefinition因为参数传递给了getHandlerFor声明类型为 RouteDefinition .

另一方面，thenReturn方法被赋予类型为 IHandleRoute<TestRoute> 的参数而它期望一个 IHandleRoute<RouteDefinition> ，这是 OngoingStubbing 的类型参数较早前提过。因此编译器错误。

要解决这个问题，最简单的方法可能是更改 route 的声明类型成为TestRoute :

TestRoute route = new TestRoute();

IRouteHandlerRegistry registry = mock(IRouteHandlerRegistry.class);
IHandleRoute<TestRoute> handler = mock(IHandleRoute.class);

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