add error pathway and test case for validation

src/loaders/ApiBasedRepositoryLoader.ts

@@ -1,6 +1,13 @@
 import { GetterSetterRepository } from "../repositories/GetterSetterRepository";
 import { IEta, IRoute, IShuttle, IStop, ISystem } from "../entities/entities";
 
+export class ApiResponseError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "ApiResponseError";
+  }
+}
+
 export class ApiBasedRepositoryLoader {
   readonly supportedSystemIds = ["263"];
   readonly baseUrl = "https://passiogo.com/mapGetData.php";
@@ -15,20 +22,32 @@ export class ApiBasedRepositoryLoader {
       getSystems: "2",
     };
     const query = new URLSearchParams(params).toString();
-    const response = await fetch(`${this.baseUrl}?${query}`);
-    const json = await response.json()
 
-    if (typeof json.all === "object") {
-      // filter down to supported systems
-      const filteredSystems = json.all.filter((jsonSystem: any) => this.supportedSystemIds.includes(jsonSystem.id));
-      await Promise.all(filteredSystems.map(async (system: any) => {
-        const constructedSystem: ISystem = {
-          id: system.id,
-          name: system.fullname,
-        };
+    try {
+      const response = await fetch(`${this.baseUrl}?${query}`);
+      const json = await response.json();
 
-        await this.repository.addOrUpdateSystem(constructedSystem);
-      }));
+      if (!response.ok) {
+        throw new Error(`HTTP error with status ${response.status}`)
+      }
+
+      if (typeof json.all === "object") {
+        // filter down to supported systems
+        const filteredSystems = json.all.filter((jsonSystem: any) => this.supportedSystemIds.includes(jsonSystem.id));
+        await Promise.all(filteredSystems.map(async (system: any) => {
+          const constructedSystem: ISystem = {
+            id: system.id,
+            name: system.fullname,
+          };
+
+          await this.repository.addOrUpdateSystem(constructedSystem);
+        }));
+      } else {
+        throw new Error("Received JSON object does not contain `all` field")
+      }
+    } catch(e: any) {
+      console.error("fetchAndUpdateSystemData call failed: ", e);
+      throw new ApiResponseError(e.message);
     }
   }