diff --git a/backend/src/interfaces/learning-content.ts b/backend/src/interfaces/learning-content.ts
index 89a1340c..5d11d6b2 100644
--- a/backend/src/interfaces/learning-content.ts
+++ b/backend/src/interfaces/learning-content.ts
@@ -65,7 +65,7 @@ export interface LearningObjectMetadata {
     uuid: string;
     hruid: string;
     version: number;
-    language: string;
+    language: Language;
     title: string;
     description: string;
     difficulty: number;
diff --git a/backend/src/services/learning-objects/dwengo-api-learning-object-provider.ts b/backend/src/services/learning-objects/dwengo-api-learning-object-provider.ts
index bef08dfe..628f616c 100644
--- a/backend/src/services/learning-objects/dwengo-api-learning-object-provider.ts
+++ b/backend/src/services/learning-objects/dwengo-api-learning-object-provider.ts
@@ -107,7 +107,7 @@ const dwengoApiLearningObjectProvider: LearningObjectProvider = {
             }
         );
 
-        if (!metadata) {
+        if (!metadata || typeof metadata !== "object") {
             console.error(`⚠️ WARNING: Learning object "${id.hruid}" not found.`);
             return null;
         }
diff --git a/backend/tests/services/learning-objects/learning-object-service.test.ts b/backend/tests/services/learning-objects/learning-object-service.test.ts
new file mode 100644
index 00000000..2c2efd1a
--- /dev/null
+++ b/backend/tests/services/learning-objects/learning-object-service.test.ts
@@ -0,0 +1,80 @@
+import {beforeAll, describe, expect, it} from "vitest";
+import {setupTestApp} from "../../setup-tests";
+import {LearningObject} from "../../../src/entities/content/learning-object.entity";
+import {getLearningObjectRepository} from "../../../src/data/repositories";
+import learningObjectExample from "../../test-assets/learning-objects/pn_werkingnotebooks/pn-werkingnotebooks-example";
+import learningObjectService from "../../../src/services/learning-objects/learning-object-service";
+import {LearningObjectIdentifier} from "../../../src/interfaces/learning-content";
+import {Language} from "../../../src/entities/content/language";
+import {EnvVars, getEnvVar} from "../../../src/util/envvars";
+
+const TEST_LEARNING_OBJECT_TITLE = "Test title";
+const EXPECTED_DWENGO_LEARNING_OBJECT_TITLE = "Werken met notebooks";
+const DWENGO_TEST_LEARNING_OBJECT_ID: LearningObjectIdentifier = {
+    hruid: "pn_werkingnotebooks",
+    language: Language.Dutch,
+    version: 3
+};
+
+async function initExampleData(): Promise<LearningObject> {
+    const learningObjectRepo = getLearningObjectRepository();
+    let learningObject = learningObjectExample.createLearningObject();
+    learningObject.title = TEST_LEARNING_OBJECT_TITLE
+    await learningObjectRepo.save(learningObject);
+    return learningObject;
+}
+
+describe("LearningObjectService", () => {
+    let exampleLearningObject: LearningObject;
+
+    beforeAll(async () => {
+        await setupTestApp();
+        exampleLearningObject = await initExampleData();
+    });
+
+    describe("getLearningObjectById", () => {
+        it("returns the learning object from the Dwengo API if it does not have the user content prefix", async () => {
+            const result = await learningObjectService.getLearningObjectById(DWENGO_TEST_LEARNING_OBJECT_ID);
+            expect(result).not.toBeNull();
+            expect(result?.title).toBe(EXPECTED_DWENGO_LEARNING_OBJECT_TITLE);
+        });
+        it("returns the learning object from the database if it does have the user content prefix", async () => {
+            const result = await learningObjectService.getLearningObjectById(exampleLearningObject);
+            expect(result).not.toBeNull();
+            expect(result?.title).toBe(exampleLearningObject.title);
+        });
+        it("returns null if the hruid does not have the user content prefix and does not exist in the Dwengo repo", async () => {
+            const result = await learningObjectService.getLearningObjectById({
+                hruid: "non-existing",
+                language: Language.Dutch
+            });
+            expect(result).toBeNull();
+        });
+    });
+
+    describe("getLearningObjectHTML", () => {
+        it("returns the expected HTML when queried with the identifier of a learning object saved in the database", async () => {
+            const result = await learningObjectService.getLearningObjectHTML(exampleLearningObject);
+            expect(result).not.toBeNull();
+            expect(result).toEqual(learningObjectExample.getHTMLRendering());
+        });
+        it("returns the same HTML as the Dwengo API when queried with the identifier of a learning object that does " +
+            "not start with the user content prefix", async () => {
+            const result = await learningObjectService.getLearningObjectHTML(DWENGO_TEST_LEARNING_OBJECT_ID);
+            expect(result).not.toBeNull();
+
+            const htmlFromDwengoApi = await fetch(
+                getEnvVar(EnvVars.LearningContentRepoApiBaseUrl)
+                + `/learningObject/getRaw?hruid=${DWENGO_TEST_LEARNING_OBJECT_ID.hruid}&language=${DWENGO_TEST_LEARNING_OBJECT_ID.language}&version=${DWENGO_TEST_LEARNING_OBJECT_ID.version}`
+            ).then(it => it.text());
+            expect(result).toEqual(htmlFromDwengoApi);
+        });
+        it("returns null when queried with a non-existing identifier", async () => {
+            const result = await learningObjectService.getLearningObjectHTML({
+                hruid: "non_existing_hruid",
+                language: Language.Dutch
+            });
+            expect(result).toBeNull();
+        });
+    });
+});