Check CONTRIBUTING guideline first and here is the list to help us investigate the problem.

Is your feature request related to a problem? Please describe.

Currently, AppVeyor CI is always failing.
We should pay attention to AppVeyor CI.

Describe the solution you'd like

Fix AppVeyor CI with several PRs.

Describe alternatives you've considered

We should mark omittable testcases for hard to fix.

Additional context

This makes obscure whether Fluentd on Windows works well or not.