### What problem does this PR solve?
Testcase for get_message_content api.
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
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Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
### What problem does this PR solve?
Web API testcase for list_messages, get_recent_message.
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
---------
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>