packages.el

(defun abclj--other-ns (ns)
  "If `ns' ends in `-test', strip that off. Otherwise, add `-test'."
  (if (string-match-p "-test$" ns)
      (string-remove-suffix "-test" ns)
    (concat ns "-test")))

(defun abclj-jump-to-test-ns-or-back (&optional arg)
  "If the point is in `project.namespace', jump to `project.namespace-test'. If
the point is in `project.namespace-test', jump to `project.namespace'."
  (interactive "P")
  (let ((target-ns (abclj--other-ns (cider-current-ns))))
    (cider-find-ns arg target-ns)))