what's the best way to satisfy this Midje test?

newb.clj

(facts "about finding sub-words"
  (fact "(sub-words) finds all possible sub-words"
    (sub-words "monocarp") => ["mono",
                               "monoc",
                               "monoca",
                               "monocar",
                               "onoc",
                               "onoca",
                               "onocar",
                               "onocarp",
                               "noca",
                               "nocar",
                               "nocarp",
                               "ocar",
                               "ocarp",
                               "carp"]))

There are more efficient ways to do it that just iterate over the correct bounds, but I quite like:

(defn sub-words
  ([^String s] (sub-words s 4))
  ([^String s ^Integer min-length]
   (vec (for [start (range 0 (.length s))
              length (range min-length (.length s))
              :let [end (+ start length)]
              :when (<= end (.length s))]
          (subs s start end)))))

But even in your example, if you find yourself filtering the results of a for then you might sometimes look at using :let and :when.