Spock test for save() method and setDefaultFormFieldConfig()

Hey guys, I am new in spock and i have problems with writing tests for save method and setDefaultFormFieldConfig(). Could You help me? i don't know what is wrong with my test.

@Override
    public FormConfig save(FormConfig formConfig, Long categoryId) {
        setDefaultFormFieldConfig(formConfig, "title", "offer.label.title", FieldType.INPUT);
        setDefaultFormFieldConfig(formConfig, "shortDescription", "offer.label.shortDescription", FieldType.TEXTAREA);
        formConfig.setCategory(categoryService.findById(categoryId));
        return formConfigRepository.save(formConfig);
    }
private void setDefaultFormFieldConfig(FormConfig formConfig, String name, String label, FieldType type) {
        if (formConfig.getFieldsConfig().stream()
                .noneMatch(fieldConfig -> fieldConfig.getName().equals(name))) {
            formConfig.getFieldsConfig()
                    .add(new FieldConfig(name, label, null, "MATCH",
                            type, false, false, true, null));
        }
    }

Test for save method:

def 'test save formConfig without defaults fields'() {
    given:
    def formConfig = Mock(FormConfig)
    formConfig.getFieldsConfig() >> new ArrayList<FieldConfig>()
    def formConfigRepository = Mock(FormConfigRepository);
    def categoryService = Mock(CategoryService);
    def impl = new FormConfigServiceImpl(formConfigRepository, categoryService)
    formConfigRepository.save(_) >> new FormConfig()
    categoryService.findById(_) >> new Category()

    when:
    impl.save(formConfig, 1)

    then:
    1 * formConfig.getFieldsConfig().add(_)
    2 * formConfig.setCategory(_)
}

And in the console I get these errors:

Too few invocations for:

1 * formConfig.getFieldsConfig().add(_)   (0 invocations)

Unmatched invocations (ordered by similarity):

None

Too few invocations for:

2 * formConfig.setCategory(_)   (1 invocation)

Unmatched invocations (ordered by similarity):

None



    at org.spockframework.mock.runtime.InteractionScope.verifyInteractions(InteractionScope.java:98)
    at org.spockframework.mock.runtime.MockController.leaveScope(MockController.java:77)
    at pl.anik.technology.book.everything.offer.service.impl.FormConfigServiceImplSpec.test save formConfig without defaults fields(FormConfigServiceImplSpec.groovy:24)


Process finished with exit code -1

Could You help me?