Java 返回 Optional<T> 的方法的 Mockito 错误
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Mockito error with method that returns Optional<T>
提问by Yu Lin Chen
I have an interface with the following method
我有一个具有以下方法的接口
public interface IRemoteStore {
<T> Optional<T> get(String cacheName, String key, String ... rest);
}
The instance of the class implementing the interface is called remoteStore.
实现该接口的类的实例称为 remoteStore。
When I mock this with mockito and use the method when:
当我用 mockito 模拟它并在以下情况下使用该方法时：
Mockito.when(remoteStore.get("a", "b")).thenReturn("lol");
I get the error:
我收到错误：
Cannot resolved the method 'thenReturn(java.lang.String)'
无法解析方法“thenReturn(java.lang.String)”
I thought it has to do with the fact that get returns an instance of the Optional class so I tried this:
我认为这与 get 返回 Optional 类的实例有关，所以我尝试了这个：
Mockito.<Optional<String>>when(remoteStore.get("cache-name", "cache-key")).thenReturn
(Optional.of("lol"));
But, I get this error instead:
但是，我收到了这个错误：
when (Optional '<'String'>') in Mockito cannot be applied to (Optional'<'Object'>').
当 Mockito 中的 (Optional '<'String'>') 不能应用于 (Optional'<'Object'>') 时。
The only time it worked was with this:
它唯一有效的时间是这样的：
String returnCacheValueString = "lol";
Optional<Object> returnCacheValue = Optional.of((Object) returnCacheValueString);
Mockito.<Optional<Object>>when(remotestore.get("cache-name", "cache-key")).thenReturn(returnCacheValue);
But above returns an instance of Optional '<'Object'>' and not Optional '<'String'>.
但上面返回一个可选的'<'Object'>'而不是可选的'<'String'>的实例。
Why couldn't I just return an instance of Optional '<'String'>' directly? If I could, how should I go about doing that?
为什么我不能直接返回 Optional '<'String'>' 的实例？如果可以，我该怎么做？
采纳答案by Makoto
Mocks that return have the expectation that the return type matches the mocked object's return type.
返回的模拟期望返回类型与模拟对象的返回类型匹配。
Here's the mistake:
这是错误：
Mockito.when(remoteStore.get("a", "b")).thenReturn("lol");
"lol"isn't an Optional<String>, so it won't accept that as a valid return value.
"lol"不是Optional<String>，所以它不会接受它作为有效的返回值。
The reason it worked when you did
当你这样做时它起作用的原因
Optional<Object> returnCacheValue = Optional.of((Object) returnCacheValueString);
Mockito.<Optional<Object>>when(remotestore.get("cache-name", "cache-key")).thenReturn(returnCacheValue);
is due to returnCacheValuebeing an Optional.
是由于returnCacheValue是Optional.
This is easy to fix: just change it to an Optional.of("lol")instead.
这很容易解决：只需将其更改为 an 即可Optional.of("lol")。
Mockito.when(remoteStore.get("a", "b")).thenReturn(Optional.of("lol"));
You can also do away with the type witnesses as well. The result above will be inferred to be Optional<String>.
您也可以取消类型见证人。上面的结果将被推断为Optional<String>。
回答by Don Bottstein
Not sure why you are seeing errors, but this compiles/runs error-free for me:
不知道为什么你会看到错误，但这对我来说编译/运行没有错误：
public class RemoteStoreTest {
public interface IRemoteStore {
<T> Optional<T> get(String cacheName, String key);
}
public static class RemoteStore implements IRemoteStore {
@Override
public <T> Optional<T> get(String cacheName, String key) {
return Optional.empty();
}
}
@Test
public void testGet() {
RemoteStore remoteStore = Mockito.mock(RemoteStore.class);
Mockito.when( remoteStore.get("a", "b") ).thenReturn( Optional.of("lol") );
Mockito.<Optional<Object>>when( remoteStore.get("b", "c") ).thenReturn( Optional.of("lol") );
Optional<String> o1 = remoteStore.get("a", "b");
Optional<Object> o2 = remoteStore.get("b", "c");
Assert.assertEquals( "lol", o1.get() );
Assert.assertEquals( "lol", o2.get() );
Mockito.verify(remoteStore);
}
}
