Email Inbox

Overview

You are given a simple email mailbox model with methods for adding messages, moving them between folders, filtering, and iterating. The code has 4 bugs that cause incorrect behavior.

Bugs

The following methods have issues:

• add_message() — ignores the message's initial folder
• move_to_folder() — leaves a copy in the old folder
• filter() — returns wrong results when combining sender and unread filters
• iter_folder() — exposes internal state to callers

Scoring

Each test is worth equal points. Your score is the percentage of tests passed.