test: add test for #41 and #42

[Miyoshi-Ryota]

I have also checked that that the test is failed without #41.

test client::tests::server_check_by_known_hosts_for_hostname ... FAILED

[Miyoshi-Ryota]

@cybersoulK
For your information, I've added tests for your works #41 and #42.
I thought this would be helpful for how to add tests, so I mention you.

To run the tests, simply install docker and run the shell script ./tests/run_unit_tests.sh.
(Unfortunately, it doesn't seem to work on the M1 Mac you're probably using.😭)