fixed tests after changes to request caching

src/app/core/cache/server-sync-buffer.effects.spec.ts

@@ -47,7 +47,7 @@ describe('ServerSyncBufferEffects', () => {
         { provide: RequestService, useValue: getMockRequestService() },
         {
           provide: ObjectCacheService, useValue: {
-            getBySelfLink: (link) => {
+            getObjectBySelfLink: (link) => {
               const object = new DSpaceObject();
               object.self = link;
               return observableOf(object);