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/Context/State/Code/ApplicationCode.ts

@@ -21,9 +21,9 @@ export class ApplicationCode implements IApplicationCode {
     private readonly scriptingDefinition: IScriptingDefinition,
     private readonly generator: IUserScriptGenerator = new UserScriptGenerator(),
   ) {
-    if (!userSelection) { throw new Error('userSelection is null or undefined'); }
-    if (!scriptingDefinition) { throw new Error('scriptingDefinition is null or undefined'); }
-    if (!generator) { throw new Error('generator is null or undefined'); }
+    if (!userSelection) { throw new Error('missing userSelection'); }
+    if (!scriptingDefinition) { throw new Error('missing scriptingDefinition'); }
+    if (!generator) { throw new Error('missing generator'); }
     this.setCode(userSelection.selectedScripts);
     userSelection.changed.on((scripts) => {
       this.setCode(scripts);

src/application/Context/State/Code/Generation/UserScriptGenerator.ts

@@ -17,8 +17,8 @@ export class UserScriptGenerator implements IUserScriptGenerator {
     selectedScripts: ReadonlyArray<SelectedScript>,
     scriptingDefinition: IScriptingDefinition,
   ): IUserScript {
-    if (!selectedScripts) { throw new Error('undefined scripts'); }
-    if (!scriptingDefinition) { throw new Error('undefined definition'); }
+    if (!selectedScripts) { throw new Error('missing scripts'); }
+    if (!scriptingDefinition) { throw new Error('missing definition'); }
     if (!selectedScripts.length) {
       return { code: '', scriptPositions: new Map<SelectedScript, ICodePosition>() };
     }