Committed a patch last night changing some tests to expect error messages that are nowhere to seen in tcl 8.4, which prompted some confusion.
Just added a comment to partcl's README which will hopefully explain:
Note that we are targetting Tcl's cvs-latest, which is going to be 8.5. This allows us to test against what will likely be state of the art by the time we approach completion. As we get closer to that day, we'll probably settle down and code against the most recent version (which hopefully won't be 9.x by then).
This has the disadvantage that for side by side testing, you'll need to build your own tcl. Partcl users don't need to worry about this, and even most partcl developers can simply code against the test suite.