Update testing guidelines in AGENTS.md to include comprehensive proxy tests for HLS playlists and error handling

AGENTS.md

@@ -58,8 +58,8 @@ As an HTML templating engine, you can use Jinja2, which is built into Flask, for
 - tests/ - folder for tests that will check critical application paths such as URL parsing, caching, playlist and segment proxying, and error handling.
     1. functions tests
     2. integration tests for the main application flow: 
-        signle integration test that will consist of server serving a single test video (use ffmpeg for generating it). it should query that server over proxy and check if it works properly.
-        yt-dlp expects from the server a javascript player that it can recognize. also server should set a cookie on the video page and require that cookie for the HLS playlist and segments requests. this will ensure that only requests coming from the video page can access the HLS content, providing a basic level of security and preventing unauthorized access to the video streams.
+        - test that the proxy can successfully retrieve and return HLS playlists and segments for valid video URLs. http logging should display when type of url is parsed and served, and when cache is hit or missed. test should also print out the headers and parial content of the playlist and segment responses (as hex) to verify that they are correct and contain expected data.
+        - test that the proxy correctly handles invalid URLs, unsupported platforms, and other error scenarios, returning appropriate HTTP error responses.
 - templates/index.html - simple HTML file with form for video URL input.
 - templates/player.html - HTML file with HLS player that will be used to play video obtained through proxy.
 - requirements.txt