Junit test list returns null even when objects inside the list have been mocked

Question

I am using Junit4 and Mockito to test some logic.

After I run the test method, the result is returning an empty list of an object while I have mocked objects and add to the list. It should have one object in the result list.

I have tried to debug the test and still see that the result list does not contain any object. The following code is just to simulate the real code that I have but they are basically the same idea.

This is the method that I want to test: a new list is created inside the method and then there are some filter going on to add items in the list and then return the result.

public List<TemplateDto> getTemplates(String name) {
        List<TemplateDto> result = new ArrayList<>();

        result.addAll(
                template.getTemplates().stream().filter(t -> t.getName().equals(name))
                .map(s -> new TemplateDto(s.getId(),s.getName()))
                .collect(Collectors.toList())
        );

        return result;
    }

This is the test method logic. I mocked one object, expecting the result to return the same object

    @Test
    public void getTemplates() {
        classToTest = mock(ClassToTest.class);
        Template template1 = new Template(1,"template1");
        List<Template> templates = new ArrayList<>();
        templates.add(template1);
        template = mock(Template.class);
        when(template.getTemplates()).thenReturn(templates);

        List<TemplateDto> result = classToTest.getTemplates("template1");
        assertEquals(result.get(0).getName(),"template1");
    }

The test should pass but instead, it fails with the following error:

java.lang.IndexOutOfBoundsException: Index: 0, Size: 0

Is there anything else that I need to mock to get the expected result?

Answer 1

1) You never mock class under test

2) You have to set the mocked value on the class under test

    classToTest = new ClassToTest();
    template = mock(Template.class);
    classToTest.setTemplate(template);
    when(template.getTemplates()).thenReturn(templates);

    List<TemplateDto> result = classToTest.getTemplates("template1");