Sitecore Unit Testing Trouble w/ NSubstitute and Nunit

Question

I am newer to Sitecore and extremely new to its unit testing. been following examples online that mimic exactly what I am trying to accomplish but I seem to be getting an object reference(you will see the error in the screenshots) not set to an instance for an item that I am passing through a function on the unit test and in the function. We had other contracted Sitecore developers on the project in the past write unit tests the same way I am here but their unit tests are passing while throwing that object reference error from their tests. I am working on a Sitecore 10.1 project solution, not that it matter in this situation i think. I am attaching screenshots for clarity on the errors and stack traces. Is this normal for how the unit tests are supposed to be working with Nsubstitute and Sitecore, maybe I am missing the point with how Sitecore works with Unit tests. Please let me know your thoughts :)

        private Item CreateItem(Database database = null)
    {
        var db = database ?? Substitute.For<Database>();

        var item = Substitute.For<Item>(ID.NewID, ItemData.Empty, db);
        var fields = Substitute.For<FieldCollection>(item);
        item.Fields.Returns(fields);

        db.GetItem(item.ID).Returns(item);
        db.GetItem(item.ID.ToString()).Returns(item);

        return item;
    }

    private void SetItemField(Item item, string fieldName, string fieldValue)
    {
        item[fieldName].Returns(fieldValue);

        var field = Substitute.For<Field>(ID.NewID, item);
        field.Database.Returns(item.Database);
        field.Value = fieldValue;
        item.Fields[fieldName].Returns(field);
    }

It seems to be something wrong with how I am setting up the unit tests itself but I have included the whole run through for clarity. If you have any other suggestions for unit testing with Sitecore, I am very open to learning new things with Sitecore :)

Answer 1

You're moving in the right direction. You should keep in mind that you can call only mocked methods. The SetItemField method is configured to return field by name:

item.Fields[fieldName].Returns(field);

... while the GetRelatedContent method tries to retrieve the field via ID:

MultilistField selectedItems = new MultilistField(
    documentItem.Fields[Templates.Document.Fields.RelatedDocuments]);

In order to get the field, the following code should be used:

var multilistField = new MultilistField(documentItem.Fields["RelatedDocument"]);
Assert.Equal(2, multilistField.Count); //pass

In order to get fields by name or id, the SetItemField method can be extended with (for instance) optional fieldId parameter:

private void SetItemField(Item item, string fieldName, string fieldValue, ID fieldId = null)
{
    fieldId = fieldId ?? ID.NewID; // new line

    item[fieldName].Returns(fieldValue);
    item[fieldId].Returns(fieldValue);  // new line

    var field = Substitute.For<Field>(fieldId, item);
    field.Database.Returns(item.Database);
    field.Value = fieldValue;
    item.Fields[fieldName].Returns(field);
    item.Fields[fieldId].Returns(field); // new line
}

Now the field can be retrieved via ID as well:

var RelatedDocumentFieldId = ID.NewID;
SetItemField(documentItem, "RelatedDocument", $"{item1.ID}|{item2.ID}", RelatedDocumentFieldId);
var multilistField = new MultilistField(
    documentItem.Fields[RelatedDocumentFieldId]);
Assert.Equal(2, multilistField.Count); // pass