Writing Test case for Generic interface with default method

I'm trying to write test cases for the interface with default method
Interface:

public interface XYZConverter <D extends DomainClass, E Extends EntityClass>{
   E createFrom(D dto);
   E updateEntity(E entity, D dto);
   
   default dtos.stream().map(this::createFrom).collect(Collectors.toList());
}

and my test class be like:

public class XYZConverterTest<D,E>{

    XYZConverter converter = spy(XYZConverter.class);
    
@Mock
DomainClass domainClass;

@Mock
EntityClass entityClass;

@BeforeEach
void setUp(){
  MockitoAnnotations.openMocks(this);
  domainClass = getDomainClass();
entityClass = getEntityClass();
 
}

@Test
void createFromDtos(){
  EntityClass = getEntityClass();
  domainClass = getDomainClass();
  Mockito.when(converter.createFromDtos(Collection<D> domainClass)).thenReturn(List.of(entityClass));
}
}

I tried to create test cases but had no luck if anyone can help me with writing test cases?

The key idea with using mocks to test is that you should never mock what is being tested, only other methods or classes that are used incidentally. In this case, the createFromDtos method should not be mocked, but the createFrom method that it uses can be.

For example:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.Spy;
import org.mockito.junit.MockitoJUnitRunner;

import java.util.List;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.when;

@RunWith(MockitoJUnitRunner.class)
public class XYZConverterTest {

    @Spy
    XYZConverter<DomainClass, EntityClass> converter;

    @Mock
    DomainClass domainClass;

    @Mock
    EntityClass entityClass;

    @Test
    public void createFromDtos() {
        when(converter.createFrom(domainClass)).thenReturn(entityClass);
        List<EntityClass> converted = converter.createFromDtos(List.of(domainClass));
        assertEquals(List.of(entityClass), converted);
    }
}