gistfile1.el

(defun clojure-in-tests-p ()
  (or (string-match-p "test\." (clojure-find-ns))
      (string-match-p "/test" (buffer-file-name))))

(defun midje-test-for (namespace)
  (let* ((namespace (clojure-underscores-for-hyphens namespace))
         (segments (split-string namespace "\\."))
         (main-namespace (first segments))
         (filename (last segments))
         (test-segments (append (list "test" main-namespace "unit") (rest (butlast segments)))))
    (concat (mapconcat 'identity test-segments "/") "/t_" (first filename))))

(defun midje-jump-to-test ()
  "Jump from implementation file to test."
  (interactive)
  (find-file (format "%s/%s.clj"
                     (file-name-as-directory
                      (locate-dominating-file buffer-file-name "src/"))
                     (midje-test-for (clojure-find-ns)))))

(defun midje-implementation-for (namespace)
  (let* ((namespace (clojure-underscores-for-hyphens namespace))
         (segments (split-string (replace-regexp-in-string "t_" "" namespace) "\\.")))
    (replace-regexp-in-string "unit" "" (mapconcat 'identity segments "/"))))

(defun midje-jump-to-implementation ()
  "Jump from midje test file to implementation."
  (interactive)
  (find-file (format "%s/src/%s.clj"
                     (locate-dominating-file buffer-file-name "src/")
                     (midje-implementation-for (clojure-find-package)))))

(defun midje-jump-between-tests-and-code ()
  (interactive)
  (if (clojure-in-tests-p)
      (midje-jump-to-implementation)
    (midje-jump-to-test)))

(define-key clojure-mode-map (kbd "C-c t") 'midje-jump-between-tests-and-code)