rename get system method on shuttle repository, update tests

src/repositories/ShuttleGetterRepository.ts

@@ -1,7 +1,7 @@
 import { IEta, IOrderedStop, IRoute, IShuttle, IStop, ISystem } from "../entities/entities";
 
 export interface ShuttleGetterRepository {
-  getSystems(): Promise<ISystem[]>;
+  getSystemIfExists(): Promise<ISystem[]>;
   getSystemById(systemId: string): Promise<ISystem | null>;
 
   getStopsBySystemId(systemId: string): Promise<IStop[]>;

src/repositories/UnoptimizedInMemoryShuttleRepository.ts

@@ -16,7 +16,7 @@ export class UnoptimizedInMemoryShuttleRepository implements ShuttleGetterSetter
 
   private subscribers: ((eta: IEta) => void)[] = [];
 
-  public async getSystems() {
+  public async getSystemIfExists() {
     return this.systems;
   }