fix(backend): Foute entity-structuur van leerpaden verbeterd.

Ook testen geschreven voor LearningPathRepository en LearningObjectRepository.

backend/tests/test-utils/load-test-asset.ts

@@ -0,0 +1,10 @@
+import fs from "fs";
+import path from "node:path";
+
+/**
+ * Load the asset at the given path.
+ * @param relPath Path of the asset relative to the test-assets folder.
+ */
+export function loadTestAsset(relPath: string): Buffer {
+    return fs.readFileSync(path.resolve(__dirname, `../test-assets/${relPath}`));
+}