Add mocked test

src/__tests__/client-id.test.ts

@@ -1,8 +1,17 @@
 require("dotenv").config();
+import fetch from "cross-fetch";
 
 import { appWithClient } from "./test-common";
 
+jest.mock("cross-fetch", () => jest.fn(jest.requireActual("cross-fetch") as any));
+
 test("sanity", async () => {
   const table = await appWithClient.getTableNamed("Things");
+  const spy = (fetch as jest.Mock).mockImplementationOnce(() => {
+    return Promise.resolve(new Response(JSON.stringify({ data: [] }), { status: 200 }));
+  });
+  const clientID = spy.mock.calls[0][1]["headers"]["X-Glide-Client-ID"];
+  expect(clientID).toBeDefined();
+  expect(clientID).toEqual(process.env.GLIDE_CLIENT_ID);
   expect(table).toBeDefined();
 });