Sling model unit test with constructor

You should revisit the usage of Mocks, specially using the @Mock annotation. The WCM Mock library you are using provides a lot of test implementations, so you don't need to mock ValueMaps etc.

Next, you are creating the imgFormItem when instantiating the class, but you load your content in the setup method. Meaning that the imgFormItem does know nothing about that content. 

So your test could look like that:

class ImageFormItemImplTest {

    public final AemContext aemContext = new AemContext();


    @BeforeEach
    void setUp() {
        //registers the Sling Model to be tested, into the mock AEM Context, so it can be instantiated in the  methods.
        aemContext.addModelsForClasses(ImageFormItemImpl.class);
        //loads resource structures into the mock context, allowing the code to interact with these resources as if they were provided by a real repository.
        aemContext.load().json("/com/biomerieux/adobe/core/models/impl/imageformitem.json", "/content");
    }

    
    void getTitle() {
        final String expected = "Facebook";
        //ctx.currentResource sets the context of the mock resource to evaluate the code against,
        // so this is set to /content/imageform as that is where the mock imageform content resource is loaded.
        aemContext.currentResource("/content");

        //instantiates the ImageFormItem Sling Model by adapting it from the mock Request object.
        ImageFormItem imgFormItem = aemContext.request().adaptTo(ImageFormItem.class);

        System.out.println("imgFormItem: "+imgFormItem);
        String actual =  imgFormItem.getTitle();
        assertEquals(expected, actual);
    }
    
    void getUrl() {
    }

    void getFileReference() {
    }
}

Next, when I was able to use AEM Context I never used Constructor injection, because it did not bring any value. Using standard injections will be sufficient.