What provides the http::config proc? Does it live in a package /tcl directory, and is it named something-procs.tcl? If not you may have to use the tcl "package require" command although I've never used it. Actually, I've never even looked at it.
It seems that the require statement is in the tclwebtest shell script. The tclwebtest starts out as a shell and is converted into a tcl shell. If I include only the tcl code from it, the require statement fails to find the http package upon loading. I looked around and could not find the http package.
If I run the tclwebtest standalone it now runs for http. I am working on https next.