Adding test coverage

README.adoc

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 = Puma::Daemon
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 In version 5.0 the authors of a popular Ruby web server https://github.com/puma/puma[Puma] chose to https://github.com/puma/puma/pull/2170/files[remove the daemonization] support from Puma, because the code wasn't wall maintained, and because other and perhaps better options exist (such as `systemd`, etc), not to mention many people have switched to Kubernetes and Docker, where you want to start all servers on the foreground.
 
 And yet, something useful and simple got lost — in our humble opinion. Some folks were indeed using the `--daemonize` features, and in Ruby they are so simple to implement due to `Process.daemon(true)` system library.