The Common Lisp Cookbook – Testing

So you want to easily test the code you’re writing ? The following recipes cover how to write automated tests and see their code coverage. We also give pointers to plug those in modern continuous integration services like Travis CI and Coveralls.

We will use an established and well-designed regression testing framework called Prove. It is not the only possibility though, FiveAM is a popular one. We prefer Prove for its doc and its extensible reporters (it has different report styles and we can extend them).

Testing with Prove

Install and load

Prove is in Quicklisp:

(ql:quickload :prove)

This command installs prove if necessary, and loads it.

Write a test file

(in-package :cl-user)
(defpackage my-test
  (:use :cl
(in-package :my-test)

(subtest "Showing off Prove"
  (ok (not (find 4 '(1 2 3))))
  (is 4 4)
  (isnt 1 #\1))

Prove’s API contains the following testing functions: ok, is, isnt, is-values, is-type, like (for regexps), is-print (checks the standard output), is-error, is-expand, pass, fail, skip, subtest.

Run a test file

(prove:run #P"myapp/tests/my-test.lisp")
(prove:run #P"myapp/tests/my-test.lisp" :reporter :list)

We get an output like:

Run one test

You can directly run one test by compiling it. With Slime, use the usual C-c C-c.

More about Prove

Prove can also:

  • be run on Travis CI,
  • colorize the output,
  • report tests duration,
  • change the default test function,
  • set a treshold for slow tests,
  • invoke the CL debugger whenever getting an error during running tests,
  • integrate with ASDF so than we can execute (asdf:test-system) or (prove:run) in the REPL (such configuration is provided by cl-project, by the same author).

See Prove’s documentation !

Code coverage

A code coverage tool produces a visual output that allows to see what parts of our code were tested or not:

Generating an html test coverage output

SBCL comes with a built-in module to do code coverage analysis: sb-cover.

Coverage reports are only generated for code compiled using compile-file with the value of the sb-cover:store-coverage-data optimization quality set to 3.

;;; Load SB-COVER
(require :sb-cover)

;;; Turn on generation of code coverage instrumentation in the compiler
(declaim (optimize sb-cover:store-coverage-data))

;;; Load some code, ensuring that it's recompiled with the new optimization
;;; policy.
(asdf:oos 'asdf:load-op :cl-ppcre-test :force t)

;;; Run the test suite.
(prove:run :yoursystem-test)

Produce a coverage report, set the output directory:

(sb-cover:report "coverage/")

Finally, turn off instrumentation:

(declaim (optimize (sb-cover:store-coverage-data 0)))

You can open your browser at ../yourproject/t/coverage/cover-index.html to see the report like the capture above or like this code coverage of cl-ppcre.

Continuous testing and test coverage with Travis CI and Coveralls

Travis is a service for running unit tests in the cloud and Coveralls shows you the evolution of coverage over time, and also tells you what a pull request will do to coverage.

Thanks to cl-travis we can easily test our program against one or many Lisp implementations (ABCL, Allegro CL, SBCL, CMUCL, CCL and ECL). cl-coveralls helps to post our coverage to the service. It supports SBCL and Clozure CL with Travis CI and Circle CI.

We refer you to the lengthy and illustrated explanations of the “continuous integration” page on

You’ll find many example projects using them in the links above, but if you want a quick overview of what it looks like: