Avoid flakes in download test

e2e/helpers/downloads.ts

@@ -1,6 +1,6 @@
 import { fileURLToPath } from 'node:url';
 import { join, dirname } from 'node:path';
-import { readFile, mkdir, rm } from 'node:fs/promises';
+import { readFile, mkdir, rm, stat } from 'node:fs/promises';
 
 export const downloadDir = join(
   dirname(fileURLToPath(import.meta.url)),
@@ -11,19 +11,25 @@ export const downloadDir = join(
 await rm(downloadDir, { recursive: true, force: true });
 await mkdir(downloadDir, { recursive: true });
 
+const sleep = (ms: number) => new Promise((res) => setTimeout(res, ms));
+
 export async function waitForFile(
   name: string,
+  minimumSize: number,
   timeout: number,
 ): Promise<string> {
   const fileName = join(downloadDir, name);
   const exp = Date.now() + timeout;
 
   do {
     try {
-      return await readFile(fileName, { encoding: 'utf-8' });
-    } catch (e) {
-      await new Promise((res) => setTimeout(res, 100));
-    }
+      const { size } = await stat(fileName);
+      if (size >= minimumSize) { // wait until file has some content
+        await sleep(10); // wait a little longer to avoid partial file reads if we get unlucky with the timing
+        return await readFile(fileName, { encoding: 'utf-8' });
+      }
+    } catch {}
+    await sleep(100);
   } while (Date.now() < exp);
 
   throw new Error(`Failed to download file ${name} within ${timeout}ms`);

e2e/pages/RetroArchiveList.ts

@@ -20,7 +20,7 @@ export class RetroArchiveList extends Page {
 
   public async clickExportJson(): Promise<string> {
     await this.click(By.linkText('Export as JSON'));
-    return waitForFile(`${this.slug}-export.json`, this.explicitWaitTimeout);
+    return waitForFile(`${this.slug}-export.json`, 10, this.explicitWaitTimeout);
   }
 
   public async getArchiveLabels(): Promise<string[]> {