Add a test for join screen

app/src/components/join-screen/JoinScreen.test.js

@@ -0,0 +1,25 @@
+import { render } from '@testing-library/react';
+import JoinScreen from "./index";
+import QRCode from "qrcode.react"
+
+let qrValue;
+jest.mock('qrcode.react', () => ({ value }) => {
+  qrValue = value;
+  return null;
+})
+
+describe("Join screen", () => {
+	test("Renders code as text, QR and link", () => {
+    const { queryByText, getByRole } = render(
+      <JoinScreen roomCode="XVXV"/>
+    );
+
+    const textCode = queryByText("XVXV");
+    expect(textCode).toBeInTheDocument();
+
+    expect(qrValue).toBe("http://localhost/guest/XVXV")
+
+    const link = getByRole("link");
+    expect(link.href).toBe("http://localhost/guest/XVXV")
+  })
+})