Add more and unify tests for absent object cases

- Unify test data for nonexistence of an object/string and collection.
- Introduce more test through adding missing test data to existing tests.
- Improve logic for checking absence of values to match tests.
- Add missing tests for absent value validation.
- Update documentation to include shared test functionality.

src/domain/Category.ts

@@ -37,7 +37,7 @@ function parseScriptsRecursively(category: ICategory): ReadonlyArray<IScript> {
 
 function validateCategory(category: ICategory) {
   if (!category.name) {
-    throw new Error('undefined or empty name');
+    throw new Error('missing name');
   }
   if (
     (!category.subCategories || category.subCategories.length === 0)