Fix duplicate slash in renderInTestApp routing

Signed-off-by: James Brooks <jamesbrooks@spotify.com>

.changeset/yellow-spies-rescue.md

@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-test-utils': patch
+---
+
+Update route path for index route in `renderInTestApp` util to fix duplicate slash and ensure any nested routing behaves correctly.

packages/frontend-test-utils/src/app/renderInTestApp.test.tsx

@@ -21,6 +21,7 @@ import {
   TestApiProvider,
 } from '@backstage/frontend-test-utils';
 import { analyticsApiRef, useAnalytics } from '@backstage/frontend-plugin-api';
+import { Routes, Route } from 'react-router-dom';
 import { renderInTestApp } from './renderInTestApp';
 
 describe('renderInTestApp', () => {
@@ -65,4 +66,18 @@ describe('renderInTestApp', () => {
       ]),
     );
   });
+
+  it('should support setting different locations in the history stack', async () => {
+    renderInTestApp(
+      <Routes>
+        <Route path="/" element={<h1>Index Page</h1>} />
+        <Route path="/second-page" element={<h1>Second Page</h1>} />
+      </Routes>,
+      {
+        initialRouteEntries: ['/second-page'],
+      },
+    );
+
+    expect(screen.getByText('Second Page')).toBeInTheDocument();
+  });
 });

packages/frontend-test-utils/src/app/renderInTestApp.tsx

@@ -154,7 +154,7 @@ export function renderInTestApp(
       factory: () => {
         return [
           coreExtensionData.reactElement(element),
-          coreExtensionData.routePath('/'),
+          coreExtensionData.routePath(''),
         ];
       },
     }),