gnu: Add emacs-buttercup.

* gnu/packages/emacs.scm (emacs-buttercup): New variable.

gnu/packages/emacs.scm

@@ -12782,3 +12782,36 @@ (define-public emacs-sesman
 buffers).  While sesman can be used to manage arbitrary sessions, it primary
 targets the Emacs based IDEs (CIDER, ESS, Geiser, Robe, SLIME etc.)")
     (license license:gpl3+)))
+
+(define-public emacs-buttercup
+  (package
+    (name "emacs-buttercup")
+    (version "1.16")
+    (source
+     (origin
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/jorgenschaefer/emacs-buttercup.git")
+             (commit (string-append "v" version))))
+       (file-name (git-file-name name version))
+       (sha256
+        (base32
+         "0dckgcyzsav6ld78bcyrrygy1cz1jvqgav6vy8f6klpmk3r8xrl1"))))
+    (build-system emacs-build-system)
+    (arguments
+     `(#:tests? #t
+       #:test-command '("make" "test")
+       #:phases
+       (modify-phases %standard-phases
+         (add-after 'install 'install-bin
+           (lambda* (#:key outputs #:allow-other-keys)
+             (install-file "bin/buttercup"
+                           (string-append (assoc-ref outputs "out") "/bin"))
+             #t)))))
+    (home-page "https://github.com/jorgenschaefer/emacs-buttercup")
+    (synopsis "Behavior driven emacs lisp testing framework")
+    (description "Buttercup is a behavior-driven development framework for
+testing Emacs Lisp code.  It allows to group related tests so they can share
+common set-up and tear-down code, and allows the programmer to \"spy\" on
+functions to ensure they are called with the right arguments during testing.")
+    (license license:gpl3+)))