2htdp comes with three different kinds of tests: 

1. tests 
   This directory contains end-to-end tests for big-bang and universe.

   These tests are mostly automatic except for two of them which expect 
   some interaction (move mouse, hold key). 
   
   The expected output is mostly some sign that the test is 'done' or 
   that no random tests failed or some cpu time. Failures are indicated
   with the word failure. 

   To execute these tests, run 

      $ ./xtest in this directory 

2. utest, uchat
   These two directories contain end-to-end universe program tests. 

   To execute these tests, run 
   
     $ ./xrun in the respective directory 

   In utest, xrun pops up two world screens that show a ball moving in one
   of two canvases. Kill one world after another, then stop the universe. 
   (It may also pop up additional world state and universe state screens.) 

   In uchat, xrun pops up two chat room screens. Type in one, see the text
   appear in the other when you hit return. 

3. tests-failed 
   This directory contains tests that are currently expected to fail. 

   
