Fix bidi screenshot quality=0 being treated as 80% (#39744)

Author: karesansui-u

packages/playwright-core/src/server/bidi/bidiPage.ts

@@ -480,7 +480,7 @@ export class BidiPage implements PageDelegate {
       context: this._session.sessionId,
       format: {
         type: `image/${format === 'png' ? 'png' : 'jpeg'}`,
-        quality: quality ? quality / 100 : 0.8,
+        quality: quality !== undefined ? quality / 100 : undefined,
       },
       origin: documentRect ? 'document' : 'viewport',
       clip: {

tests/page/page-screenshot.spec.ts

@@ -394,6 +394,13 @@ it.describe('page screenshot', () => {
     expect(error.message).toContain('options.quality is unsupported for the png');
   });
 
+  it('quality option should work for jpeg', async ({ page, server }) => {
+    await page.goto(server.PREFIX + '/grid.html');
+    const zeroQuality = await page.screenshot({ type: 'jpeg', quality: 0 });
+    const highQuality = await page.screenshot({ type: 'jpeg', quality: 100 });
+    expect(zeroQuality.byteLength).toBeLessThan(highQuality.byteLength);
+  });
+
   it('should prefer type over extension', async ({ page }, testInfo) => {
     const outputPath = testInfo.outputPath('file.png');
     const buffer = await page.screenshot({ path: outputPath, type: 'jpeg' });