add cache initialization

src/repositories/ApiBasedRepository.ts

@@ -14,6 +14,19 @@ interface ApiBasedRepositoryCache {
 }
 
 export class ApiBasedRepository implements GetterRepository {
+  private cache: ApiBasedRepositoryCache;
+
+  constructor(initialCache: ApiBasedRepositoryCache | undefined = undefined) {
+    if (initialCache) {
+      this.cache = initialCache;
+    } else {
+      this.cache = {
+        etasForShuttleId: {},
+        etasForStopId: {},
+      }
+    }
+  }
+
   public async getEtaForShuttleAndStopId(shuttleId: string, stopId: string): Promise<IEta | null> {
     return null;
   }