Any methods Mockito 4.11.0 tries to stub on a class which extends an abstract groovy (2.4.21) class result in NPE for me. The following example is how I am trying to stub two methods on the Demo class, but since Demo extends an abstract class all I get are NPE, even for the method “bar()” native to Demo. Removing the word “abstract” causes the test code to execute green. Can someone help me understand what I am doing wrong here and how I can mock classes which extend groovy abstract classes?

import org.junit.Test
import org.mockito.Mockito

import static org.mockito.Mockito.when

class Demo extends Foo {

    boolean bar() {
        return false
    }
}

abstract class Foo {
    Boolean isValid() {
        return true
    }
}

class DemoTest {

    @Test
    void testMe() {
        Demo demo = Mockito.mock(Demo.class)
        when(demo.isValid()).thenReturn(false) // will throw NPE
        when(demo.bar()).thenReturn(false) // will throw NPE
    }
}