init.el

(defun jim/cider-test-is-test-ns (ns)
  (let ((suffix "-test")) 
    (string-match (rx-to-string `(: ,suffix eos) t) ns)))

(defun jim/cider-test-impl-ns-fn (ns)
  (when ns
    (let ((suffix "-test"))
      (if (string-match (rx-to-string `(: ,suffix eos) t) ns)
          (s-replace suffix "" ns)
        ns))))

(defun jim/cider-test-jump-around ()
  (interactive)
  (let ((ns (cider-current-ns)))
    (switch-to-buffer
     (cider-find-buffer
      (if (jim/cider-test-is-test-ns ns)
          (jim/cider-test-impl-ns-fn ns)
        (cider-test-default-test-ns-fn ns))))))