Extreme Programming (sometimes abbreviated as XP), is a light-weight development methodology developed by Kent Beck. There are now several books about XP.
One aspect of Extreme Programming is Test Driven Design. This is supported by the xUnit family of test frameworks. (The first of which might have been SUnit[L1 ], which supports testing with Smalltalk.)
Java has JUnit[L2 ].
Tcl has tclunit. (Tcl's built-in tcltest framework is also eminently suitable for unit testing.)
See also XotclIDE.
The Portland Pattern Repository Wiki [L3 ] has an extensive collection of pages on ExtremeProgramming [L4 ].
See http://park.ruru.ne.jp/ando/work/tclTkUnit/ for TclTkUnit , a JUnit like testing framework.
TclTkUnit appears to be a dead project, software can be accessed at archive.org http://web.archive.org/web/20091009212801/http://park.ruru.ne.jp/ando/work/tclTkUnit/ .