Mockito 在模拟 Javalin 上下文中调用真实方法

Question

I have a real strange behavior going on. It seems that Mockito is calling the real method on a mocked class, resulting in a NullPointerException. I am mocking the Context object present in the Javalin http framework for Java.

This is the minimal code that results in an exception.

import io.javalin.http.Context;
import org.mockito.Mockito;

public class Main {
    public static void main(String[] args) {
        Context ctx = Mockito.mock(Context.class);
        Mockito.when(ctx.queryParam("hello")).thenReturn("test");
    }
}

I get

    at io.javalin.http.Context.queryString(Context.kt:285)
    at io.javalin.http.Context.queryParamMap(Context.kt:282)
    at io.javalin.http.Context.queryParams(Context.kt:279)
    at io.javalin.http.Context.queryParam(Context.kt:266)
    at io.javalin.http.Context.queryParam$default(Context.kt:266)
    at io.javalin.http.Context.queryParam(Context.kt)
    at Main.main(Main.java:9)

But its not supposed to call the real code? What is going on?

Answer 1

You're not really adding tests correctly. Instead of creating them in the main method, create a test class and then annotate your tests with the @Test annotation (will need JUnit for this). You should then be able to run the tests using your IDE.

Answer 2

Yes I know that I am supposed to use this in a test. I just showed that snipped to show what does not work. The fault here turned out to be that Mockito is written in Kotlin which by default makes all methods final when exposing a Java api. Mockito does not work with final methods and that is why this does not work. You simply can't mock Kotlin frameworks with Mockito, you have to use something else.