"resource.adaptTo" NullPointer Unit test AEM Sling Model Java

I'm doing a pretty basic Unit test for Sling Model in AEM, so, when I run the test I get the following error:

[ERROR] CtaModelTest.testGetText:36 NullPointer

This is my Java code, the Model is a very basic Sling AEM Model, I'm using the @ModelAnnotation as follow:

@Model(adaptables = SlingHttpServletRequest.class, defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)

package com.myproject.core.models;
import org.apache.commons.lang3.StringUtils;
import org.apache.sling.api.resource.Resource;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import com.day.cq.wcm.api.Page;
import io.wcm.testing.mock.aem.junit5.AemContext;
import io.wcm.testing.mock.aem.junit5.AemContextExtension;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertTrue;
import junitx.util.PrivateAccessor;
import javax.inject.Inject;

@ExtendWith(AemContextExtension.class)
class CtaModelTest {
    private static final String COMPONENT_PATH = "/content/campaigns/myproject/master/demo-campaign/demo-email";
    
    private CtaModel ctaModel;

    private Page page;
    private Resource resource;

    @BeforeEach
    public void setup(AemContext context) throws Exception {
        
        context.load().json("/ctaModelTest.json", COMPONENT_PATH);
        context.addModelsForClasses(CtaModel.class);
        
        resource = context.resourceResolver().getResource(COMPONENT_PATH + "/jcr:content/par/hero/cta");
        ctaModel = resource.adaptTo(CtaModel.class);
    }

    @Test
    void testGetText() throws Exception {
        String txt = ctaModel.getText();
        assertNotNull(txt);
    }
}

Can anyone help me to fix it?

Solution

It seems that resource.adaptTo(CtaModel.class) returned null. The problem is, that adaptTo(...) returns null very silently, if anything fails. Therefore the SlingMocks documentation recommends ModelFactory.createModel(...) instead of adaptTo(...) for SlingModels.

https://sling.apache.org/documentation/development/sling-mock.html#model-instantiation

// load some content into the mocked repo
context.load().json(..., "/resource1");

// load resource
Resource myResource = content.resourceResolver().getResource("/resource1");

// instantiate Sling Model (adaptable via Resource)
// this will throw exceptions if model cannot be instantiated
MyModel myModel = context.getService(ModelFactory.class).createModel(myResource, MyModel.class);

If you doing this, the ModelFactory will log error-details, why the Sling model couldn't be created. So you know, what the problem is, and you don't need to guess.