Add tests

[soutaro]

This PR is to add tests for the rake tasks for minitest and the VS Code extension.

• The tests for rake tasks are saved in ruby/test/minitest directory. It runs rake tasks and verifies the outputs.
• The tests for extension are saved in test directory. It tests RubyAdapter with DummyController which saves all of the events triggered by the adapter.

I added only tests for minitest, but it would be easy to add scripts for rspec and more. (I'm interested in supporting Test::Unit.)

This PR is an example on my fork to show you how CI results look like.