added test coverage for throw custom error

test/exceptionshandling.test.js

@@ -0,0 +1,30 @@
+import process from 'node:process';
+import dotenv from 'dotenv';
+import {describe, expect, it} from 'vitest';
+import {initializeClient} from './setup.js';
+
+dotenv.config();
+
+const username = process.env.ZENDESK_USERNAME;
+const token = process.env.ZENDESK_TOKEN;
+
+describe('Zendesk Exceptions Handling', () => {
+  it('should throw an error for an invalid subdomain', async () => {
+    const error = new Error('My Custom Error');
+    error.details = 'Custom Details';
+
+    const client = initializeClient({
+      username,
+      token,
+      subdomain: 'any',
+      throwOriginalException: true,
+      transportConfig: {
+        transportFn() {
+          throw error;
+        },
+      },
+    });
+
+    await expect(() => client.users.me()).rejects.toThrowError(error);
+  });
+});