docs(python): add example for testing Chromium extensions (#7338)

docs/src/chrome-extensions.md

@@ -27,3 +27,58 @@ const { chromium } = require('playwright');
   await browserContext.close();
 })();
 ```
+
+```python async
+import asyncio
+from playwright.async_api import async_playwright
+
+path_to_extension = "./my-extension"
+user_data_dir = "/tmp/test-user-data-dir"
+
+
+async def run(playwright):
+    context = await playwright.chromium.launch_persistent_context(
+        user_data_dir,
+        headless=False,
+        args=[
+            f"--disable-extensions-except={path_to_extension}",
+            f"--load-extension={path_to_extension}",
+        ],
+    )
+    background_page = context.background_pages[0]
+    # Test the background page as you would any other page.
+    await context.close()
+
+
+async def main():
+    async with async_playwright() as playwright:
+        await run(playwright)
+
+
+asyncio.run(main())
+```
+
+```python sync
+from playwright.async_api import sync_playwright
+
+path_to_extension = "./my-extension"
+user_data_dir = "/tmp/test-user-data-dir"
+
+
+def run(playwright):
+    context = playwright.chromium.launch_persistent_context(
+        user_data_dir,
+        headless=False,
+        args=[
+            f"--disable-extensions-except={path_to_extension}",
+            f"--load-extension={path_to_extension}",
+        ],
+    )
+    background_page = context.background_pages[0]
+    # Test the background page as you would any other page.
+    context.close()
+
+
+with sync_playwright() as playwright:
+    run(playwright)
+```