this gives a useful test coverage of possibles connections parameters
regarding versions, ciphers, etc that the user can choose, and check
that it all lead to a TLS connected state.
The test establish a TLS connection on a socketpair, and then
check that by injecting arbitrary data in the client we receive
the exact same thing on the server side.
The test need more sophistication in general, as to arbitrarily test
TLS versions, different ciphers & key exchange, certificates, etc.
