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/Script.ts

@@ -12,7 +12,7 @@ export class Script extends BaseEntity<string> implements IScript {
   ) {
     super(name);
     if (!code) {
-      throw new Error(`undefined code (script: ${name})`);
+      throw new Error(`missing code (script: ${name})`);
     }
     validateLevel(level);
   }