gistfile1.sls

(global-set-key "\C-ct" 'toggle-test)
(defun toggle-test ()
  (interactive)
  (let* ((file-name (buffer-file-name))
         (toggle-file-name
          (cond ((string-match "\\(.*\\)/javatests/\\(.*\\)\\(/[^/]*\\)Test.java$" file-name)
                 (concat (match-string 1 file-name)
                         "/java/"
                         (match-string 2 file-name)
                         (match-string 3 file-name)
                         ".java"))
		((string-match "\\(.*\\)/java/\\(.*\\)\\(/[^/]*\\).java$" file-name)
                 (concat (match-string 1 file-name)
                         "/javatests/"
                         (match-string 2 file-name)
                         (match-string 3 file-name)
                         "Test.java")))))
    (if toggle-file-name
	(find-file toggle-file-name)
      (message "Unable to determine the toggle-test file."))))