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Usage

Buttercup is primarily meant to be used non-interactively, to automatically test a project independent of a user’s setup, before a commit and on a continuous integration platform. Because of this, the recommended workflow for buttercup does not use interactive commands but instead the command line.

Cask

Cask is a project to create an environment separate from your usual interactive Emacs environment. This allows you to install the packages your project depends on, and only those, and test your project in a well-defined environment.

Buttercup works best in such environments, so the following best practices rely on Cask to be installed.

Project Directory Layout

A basic project layout requires a project file, called feature.el here, a Cask file to define dependencies, and a tests/ directory for tests. It should look roughly like this:

feature/feature.el
        Cask
        tests/test-feature.el

feature.el

(defun featurize (bug feature)
  (format "It's not a %s, it's a %s" bug feature))

(provide 'feature)

Cask

(source gnu)
(source melpa-stable)

(development
 (depends-on "buttercup"))

tests/test-feature.el

(require 'feature)

(describe "The feature"
  (it "can use bug and feature"
    (expect (featurize "bug" "feature")
            :to-equal
            "It's not a bug, it's a feature")))

Running Tests

You can now use Cask to run your tests.

First, you have to install the dependencies. You only have to do this once, or when the dependencies change:

$ cask
Extracting buttercup-1.1/
Extracting buttercup-1.1/buttercup-compat.el
Extracting buttercup-1.1/buttercup.el
Extracting buttercup-1.1/bin/
Extracting buttercup-1.1/bin/buttercup
Extracting buttercup-1.1/buttercup-pkg.el
Generating autoloads for buttercup-compat.el...
Generating autoloads for buttercup-compat.el...done
Generating autoloads for buttercup-pkg.el...
Generating autoloads for buttercup-pkg.el...done
Generating autoloads for buttercup.el...
Generating autoloads for buttercup.el...done

Now, you can run your tests:

$ cask exec buttercup -L .
Running 1 specs.

The feature
  can use bug and feature

Ran 1 specs, 0 failed, in 0.0 seconds.

That’s it. Buttercup’s built-in discover test runner looks for files named test-*.el, *-test.el or *-tests.el. You can specify a different pattern using the --pattern command line argument to the buttercup program.

You can run this command whichever way you like. Common choices include a makefile or shell scripts.

Projectile

If you use Projectile for interacting with your projects you can set the "default" project test command to be available when you invoke projectile-test-project. Create a .dir-locals.el file in the the root of your project tree (next to your Cask file). An example:

.dir-locals.el

((nil . ((eval . (progn
                   (require 'projectile)
                   (puthash (projectile-project-root)
                            "cask exec buttercup -L ."
                            projectile-test-cmd-map))))))

Travis

If your project is hosted on github, you can use Travis CI as your continuous integration environment. Buttercup can easily be used in such a setup. Simply add the following .travis.yml file:

language: emacs-lisp
sudo: false
cache: apt
env:
  - EVM_EMACS=emacs-24.5-travis
  - EVM_EMACS=emacs-25.1-travis
before_install:
  - curl -fsSkL https://gist.github.com/rejeep/ebcd57c3af83b049833b/raw > travis.sh && source ./travis.sh
  - evm install $EVM_EMACS --use --skip
  - cask
install:
  - cask install
script:
  - emacs --version
  - cask exec buttercup -L .

Most of the complexity here is from installing EVM and Cask to be able to test your project using different Emacs versions.