added unit test for the change

src/app/shared/services/attachment.service.spec.ts

@@ -29,11 +29,25 @@ describe("AttachmentService", () => {
     });
 
     it("should return null for non-string input", () => {
-      const mimeType = service.base64MimeType(null as any);
+      const mimeType = service.base64MimeType(null);
       expect(mimeType).toBeNull();
     });
   });
 
+  describe("getImageUrl", () => {
+    it("should return the pdf icon if the file is pdf", () => {
+      const encoded = "data:application/pdf;base64,SGVsbG8sIFdvcmxkIQ==";
+      const imageUrl = service.getImageUrl(encoded);
+      expect(imageUrl).toBe("assets/images/pdf-icon.svg");
+    });
+
+    it("should return the encoded string if the file is not pdf", () => {
+      const encoded = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUA";
+      const imageUrl = service.getImageUrl(encoded);
+      expect(imageUrl).toBe(encoded);
+    });
+  });
+
   describe("openAttachment", () => {
     it("should open a new window with the correct object URL", () => {
       const encoded = "data:text/plain;base64,SGVsbG8sIFdvcmxkIQ==";

src/app/shared/services/thumbnail.service.spec.ts

@@ -5,6 +5,7 @@ import { ThumbnailService } from "./thumbnail.service";
 import { selectDatasetsPerPage } from "state-management/selectors/datasets.selectors";
 import { MockStore, provideMockStore } from "@ngrx/store/testing";
 import { of, throwError } from "rxjs";
+import { AttachmentService } from "./attachment.service";
 
 describe("ThumbnailService", () => {
   let service: ThumbnailService;
@@ -27,6 +28,9 @@ describe("ThumbnailService", () => {
           provide: AppConfigService,
           useValue: { getConfig },
         },
+        {
+          provide: AttachmentService,
+        },
         provideMockStore({
           selectors: [
             {