Extreme Programming (sometimes abbreviated as XP), is a light-weight development
methodology developed by Kent Beck.  There are now several books about XP.

   * http://www.extremeprogramming.org/

   * http://www.xprogramming.com/

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[http://ansi-st-tests.sourceforge.net/SUnit.html], which supports testing with [Smalltalk].)

Java has JUnit[http://www.junit.org/index.htm].

Tcl has [tclunit]. Tcl's build-in [tcltest] framework is also eminently suitable for unit testing.

See also [XotclIDE].