fix: added dependencies for development. feat: added axios as dependency. feat: added some initial modeals. feat: setup unit testing

src/OnspringClient.ts

@@ -1,9 +1,25 @@
-class OnspringClient {
-  private readonly _baseUrl: string;
-  private readonly _apiKey: string;
+import { AxiosInstance } from "axios";
+import axios from "axios";
+import { ArgumentValidator } from "./models/ArgumentValidator";
 
-  constructor(baseUrl: string, apiKey: string) {
-    this._baseUrl = baseUrl;
-    this._apiKey = apiKey;
+export class OnspringClient {
+  protected readonly client: AxiosInstance;
+
+  constructor(baseUrl: string | undefined | null, apiKey: string | undefined | null) {
+    if (ArgumentValidator.isValidUrl(baseUrl) === false) {
+      throw new Error("baseUrl must be an absolute and well-formed URI.");
+    }
+
+    if (ArgumentValidator.isNullOrWhiteSpace(apiKey)) { 
+      throw new Error("apiKey cannot be null/empty/whitespace.");
+    }
+
+    this.client = axios.create({
+      baseURL: baseUrl,
+      headers: {
+        "x-apikey": apiKey,
+        "x-api-version": "2",
+      },
+    });
   }
 }