This mixin class provides methods to test an the HTTP::Server::Simple
manpage-based web server. Currently, it provides only one such method:
'started_ok'.

started_ok [$text]
'started_ok' takes an optional test description. The server needs to
have been configured (specifically, its port needs to have been set),
but it should not have been run or backgrounded. 'started_ok' calls
'background' on the server, which forks it to run in the background.
the Test::HTTP::Server::Simple manpage takes care of killing the server
when your test script dies, even if you kill your test script with an
interrupt. 'started_ok' returns the URL 'http://localhost:$port' which
you can use to connect to your server.

Note that if the child process dies, or never gets around to listening
for connections, this just hangs. (This may be fixed in a future
version.)