set ::done HAND
        catch {tls::handshake $sock} msg
        set ::done $msg
    }
    # NOTE: when doing an in-process client/server test, both sides need
    # to be non-blocking for the TLS handshake

    # Server - Only accept TLS 1.3
    set s [tls::socket \
        -certfile $serverCert -cafile $caCert -keyfile $serverKey -request 0 \
	-require 0 -ssl2 0 -ssl3 0 -tls1 0 -tls1.1 0 -tls1.2 0 -tls1.3 1 \
        -server Accept 8831]
    # Client - Only propose TLS1.2
    set c [tls::socket -async -cafile $caCert -request 0 -require 0 \
	-ssl2 0 -ssl3 0 -tls1 0 -tls1.1 0 -tls1.2 1 -tls1.3 0 localhost 8831]
    fconfigure $c -blocking 0
    puts $c a ; flush $c
    after 5000 [list set ::done timeout]
    vwait ::done
    switch -exact -- $::done {
        "handshake failed: wrong ssl version" -
        "handshake failed: unsupported protocol" {
            set ::done "handshake failed: wrong version number"
        }
    }
    catch {close $c}
    catch {close $s}
    set ::done
} {handshake failed: wrong version number}

# cleanup
if {[string match sock* $commandSocket] == 1} {
   puts $commandSocket exit
   flush $commandSocket