Test Framework
Somebody once said that Lispniks have been the first agile developers, doing the stuff people now all go mad about decades ago without thinking twice. So maybe it isn't very surprising that there are quite a lot of tools that help with test driven development.

(Debatable) According to the State of Common Lisp 2015, the two following test frameworks are worth considering nowadays:

Also active in 2018 are

See also Test framework comparison.

Known Common Lisp Test Frameworks on CLiki include:

Like COVER: Common Lisp test case coverage determination tool.

clos-unit ( clos-unit appears to be deprecated in favor of xlunit which has almost the same semantics ) are basically implementations of the *Unit design (like JUnit, SUnit etc), where a test case (and a test fixture, there isn't much differentiation) is a CLOS class, and the individual tests are its methods. Failure of a test is usually indicated by calls to some assertion forms or by signaling an appropriate condition.

FiveAM seems to offer similar functionality, but handles it in another fashion. For example, setting up and tearing down a fixture isn't done with defining methods for a test-case class, but with a WITH-FIXTURE macro which simply wraps one piece of code with another.

rt is an older library from the CMU AI repository. It takes a more simplistic approach, a single test is made up of its name, a form to evaluate, and the expected return values of this form. CLUnit takes a similar approach, but with a lot more sugar, like collecting and classifying tests, giving a comparison function to match the real with the expected output etc.

testbild is not a test framework but a library designed to be used by the former that harmonizes test output styles and grants the powers of TAP.

cl-travis lets you run your tests on Travis CI.