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/DocumentationParser.ts

@@ -2,7 +2,7 @@ import { DocumentableData, DocumentationUrlsData } from 'js-yaml-loader!@/*';
 
 export function parseDocUrls(documentable: DocumentableData): ReadonlyArray<string> {
   if (!documentable) {
-    throw new Error('documentable is null or undefined');
+    throw new Error('missing documentable');
   }
   const { docs } = documentable;
   if (!docs || !docs.length) {