(For newcomers:) more tests and benchmarks

[Berrysoft]

We need more tests and benchmarks. They will help us debug and improve the code quality.

This issue is for newcomers of this project. If you would like to contribute, but don't know which work you can do, you can start with a test or a benchmark. The experience with compio will help you more familiar with the code.

See monoio and tokio-uring for reference of tests.