The Common Lisp Cookbook – Testing

Table of Contents

The Common Lisp Cookbook – Testing

🎉 New ! Get the EPUB version.

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 (see this blogpost for an introduction) and there are others (and more again). We prefer Prove for its documentation and its extensible reporters (it has different report styles and we can extend them).

warning: Prove has a couple limitations and will soon be obsolete. We advise to start with another test framework.

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:

See Prove’s documentation!

Interactively fixing unit tests

Common Lisp is interactive by nature (or so are most implementations), and testing frameworks make use of it. It is possible to ask the framework to open the debugger on a failing test, so that we can inspect the stack trace and go to the erroneous line instantly, fix it and re-run the test from where it left off, by choosing the suggested restart.

With Prove, set prove:*debug-on-error* to t.

Below is a short screencast showing all this in action (with FiveAM):

Note that in the debugger:

Code coverage

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

Such capabilities are included into Lisp implementations. For example, SBCL has the sb-cover module and the feature is also built-in in CCL or LispWorks.

Generating an html test coverage output

Let’s do it with SBCL’s 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 Integration

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:

Gitlab CI

Gitlab CI is part of Gitlab and is available on, for public and private repositories. Let’s see straight away a simple .gitlab-ci.yml:


image: clfoundation/sbcl:latest

  - install-quicklisp
  - git clone ~/quicklisp/local-projects/

    - make test

Gitlab CI is based on Docker. With image we tell it to use the latest tag of the clfoundation/sbcl image. This includes the latest version of SBCL, many OS packages useful for CI purposes, and a script to install Quicklisp. Gitlab will load the image, clone our project and put us at the project root with administrative rights to run the rest of the commands.

test is a “job” we define, script is a recognized keywords that takes a list of commands to run.

Suppose we must install dependencies before running our tests: before_script will run before each job. Here we install Quicklisp (adding it to SBCL’s init file), and clone a library where Quicklisp can find it.

We can try locally ourselves. If we already installed Docker and started its daemon (sudo service docker start), we can do:

docker run --rm -it -v /path/to/local/code:/usr/local/share/common-lisp/source clfoundation/sbcl:latest bash

This will download the lisp image (±300MB compressed), mount some local code in the image where indicated, and drop us in bash. Now we can try a make test.

Here is a more complete example that tests against several CL implementations in parallel:

  IMAGE_TAG: latest

image: clfoundation/$LISP:$IMAGE_TAG

  - test
  - build

  - install-quicklisp
  - git clone ~/quicklisp/local-projects/

  stage: test
    - make test

abcl test:
  extends: .test
    LISP: abcl

ccl test:
  extends: .test
    LISP: ccl

ecl test:
  extends: .test
    LISP: ecl

sbcl test:
  extends: .test
    LISP: sbcl

  stage: build
    LISP: sbcl
    - tags
    - make build
      - some-file-name

Here we defined two stages (see environments), “test” and “build”, defined to run one after another. A “build” stage will start only if the “test” one succeeds.

“build” is asked to run only when a new tag is pushed, not at every commit. When it succeeds, it will make the files listed in artifacts’s paths available for download. We can download them from Gitlab’s Pipelines UI, or with an url. This one will download the file “some-file-name” from the latest “build” job:

When the pipelines pass, you will see:

You now have a ready to use Gitlab CI.

Page source:

© 2002–2020 the Common Lisp Cookbook Project