Introduce integration tests

[kyu08]

tools

• https://github.com/microsoft/tui-test
• https://github.com/mitsuhiko/insta

Something I know

• insta seems that it can not handle key inputs.
• ratatui's test https://github.com/ratatui-org/ratatui/blob/main/tests/widgets_barchart.rs

How to implement

1. pass frame and model to ui
2. Check its output(using cargo-insta with snapshot file)

Reference

• ymgyt/syndicationd@72f90cb
• ratatui's test https://github.com/ratatui-org/ratatui/blob/main/tests/widgets_barchart.rs
• tui-term's test https://github.com/a-kenji/tui-term/blob/524ffb0beed9ae6e6f08f51e7c3ecfc1b716fdb5/src/widget.rs#L338-L353