test(backend): Testen voor DatabaseLearningObjectProvider.getLearningObjectHTML toegevoegd.

Hierbij optredende problemen ook opgelost.

backend/src/services/learning-objects/processing/string-processor.ts

@@ -0,0 +1,19 @@
+import Processor from "./processor";
+import {LearningObject} from "../../../entities/content/learning-object.entity";
+
+export abstract class StringProcessor extends Processor<string> {
+    /**
+     * Function which actually executes the rendering of a learning object.
+     * By default, this just means rendering the content in the content property of the learning object (interpreted
+     * as string)
+     *
+     * When implementing this function, we may assume that we are responsible for the content type of the learning
+     * object.
+     *
+     * @param toRender Learning object to render
+     * @protected
+     */
+    protected renderLearningObjectFn(toRender: LearningObject): string {
+        return this.render(toRender.content.toString("ascii"));
+    }
+}