`middleware.test`: offer fail-fast functionality

[vemv]

It would be sweet to offer fail-fast functionality. Under it:

• The first failing failing test var fails that ns; and
• The first failing ns fails the test run.

Relevant code:

https://github.com/clojure-emacs/cider-nrepl/blob/a740583c3aa8b582f3097611787a276775131d32/src/cider/nrepl/middleware/test.clj#L238-L239

https://github.com/clojure-emacs/cider-nrepl/blob/a740583c3aa8b582f3097611787a276775131d32/src/cider/nrepl/middleware/test.clj#L260-L263

Some inspiration:

(defn run-tests
  "Like clojure.test/run-tests, but fails fast."
  [& namespaces]
  (let [summary (-> (->> namespaces
                         (reduce (bound-fn [r n]
                                   (let [{:keys [fail error]
                                          :as v} (clojure.test/test-ns n)
                                         failed? (some pos? [fail error])
                                         ret (merge-with + r v)]
                                     (cond-> ret
                                       failed? reduced)))
                                 clojure.test/*initial-report-counters*))
                    (assoc :type :summary))]
    (clojure.test/do-report summary)
    summary))

[bbatsov]

Yeah, that'd be great. It has been on the TODO list for as long as the middleware existed, alongside async reporting of the progress. The fail-fast is definitely easier to implement, though.