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/application/Parser/CategoryCollectionParser.ts

@@ -29,7 +29,7 @@ export function parseCategoryCollection(
 
 function validate(content: CollectionData): void {
   if (!content) {
-    throw new Error('content is null or undefined');
+    throw new Error('missing content');
   }
   if (!content.actions || content.actions.length <= 0) {
     throw new Error('content does not define any action');