Unit
nFor purposes of unit testing with object-oriented languages, unit most often means a class.
n“Classes should contain their own tests.”
You might be wondering what a unit is supposed to be.  It is essentially a class.

The original idea is that classes should contain their own tests.  It has turned out that the testing framework in Smalltalk at least works a little better when this in not actually the case.  Test classes are kept separate from the classes being tested.