fix(front): stabilize downloadFile unit test and return promise chain (#18484)

# Description

## What this PR fixes
This PR fixes a flaky/skipped unit test for
[downloadFile](vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html)
and aligns the test with the actual implementation.

## Changes made
Updated
[downloadFile](vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html)
test to validate file-saver behavior instead of DOM anchor creation.
Mocked
[saveAs](vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html)
from file-saver and asserted it is called with the fetched blob and
filename.
Added proper async assertions for:
successful file download
failed fetch path ([status !==
200](vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html))
rejecting with Failed downloading file
Updated
[downloadFile](vscode-file://vscode-app/Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/code/electron-browser/workbench/workbench.html)
implementation to return the fetch promise chain so callers/tests can
await it reliably.

## Related Issue
Closes #18485

packages/twenty-front/src/modules/activities/files/utils/__tests__/downloadFile.test.ts

@@ -1,35 +1,39 @@
 import { downloadFile } from '@/activities/files/utils/downloadFile';
+import { saveAs } from 'file-saver';
+
+jest.mock('file-saver', () => ({
+  saveAs: jest.fn(),
+}));
+
+const mockBlob = new Blob(['test content'], { type: 'application/pdf' });
 
 global.fetch = jest.fn(() =>
   Promise.resolve({
     status: 200,
-    blob: jest.fn(),
+    blob: () => Promise.resolve(mockBlob),
   } as unknown as Response),
 );
 
-window.URL.createObjectURL = jest.fn(() => 'mock-url');
-window.URL.revokeObjectURL = jest.fn();
-
-// FIXME: jest is behaving weirdly here, it's not finding the element
-// Also the document's innerHTML is empty
-// `global.fetch` and `window.fetch` are also undefined
-describe.skip('downloadFile', () => {
-  it('should download a file', () => {
-    downloadFile('url/to/file.pdf', 'file.pdf');
-
-    expect(fetch).toHaveBeenCalledWith('url/to/file.pdf');
-
-    const link = document.querySelector(
-      'a[href="mock-url"][download="file.pdf"]',
-    );
-
-    expect(link).not.toBeNull();
-    // oxlint-disable-next-line @typescripttypescript/ban-ts-comment
-    // @ts-ignore
-    expect(link?.style?.display).toBe('none');
-
-    expect(link).toHaveBeenCalledTimes(1);
-
+describe('downloadFile', () => {
+  afterEach(() => {
     jest.clearAllMocks();
   });
+
+  it('should download a file', async () => {
+    await downloadFile('url/to/file.pdf', 'file.pdf');
+
+    expect(fetch).toHaveBeenCalledWith('url/to/file.pdf');
+    expect(saveAs).toHaveBeenCalledWith(mockBlob, 'file.pdf');
+  });
+
+  it('should reject when fetch fails', async () => {
+    (global.fetch as jest.Mock).mockResolvedValueOnce({
+      status: 404,
+      blob: () => Promise.resolve(mockBlob),
+    });
+
+    await expect(downloadFile('url/to/file.pdf', 'file.pdf')).rejects.toBe(
+      'Failed downloading file',
+    );
+  });
 });

packages/twenty-front/src/modules/activities/files/utils/downloadFile.ts

@@ -1,7 +1,7 @@
 import { saveAs } from 'file-saver';
 
 export const downloadFile = (fullPath: string, fileName: string) => {
-  fetch(fullPath)
+  return fetch(fullPath)
     .then((resp) =>
       resp.status === 200
         ? resp.blob()