 Sandboxes replicate at least the minimal functionality needed to accurately test the programs or other code under development (e.g.usage of the same environment variables as, or access to an identical database to that used by, the stable prior implementation intended to be modified; there are many other possibilities, as the specific functionality needs vary widely with the nature of the code and the application[s] for which it is intended).The concept of sandbox (sometimes also called a working directory, a test server or development server) is typically built into revision control software such as Git, CVS and Subversion (SVN), in which developers "check out" a "copy" of the source code tree, or a branch thereof, to examine and work on.