Capturing of printed lines in tests

[matthewdowney]

Sometimes I'll sprinkle printlns throughout a comment to demonstrate side effects or order of events.

Like

(comment
  (try
    (println "Happens first") 
    (throw (ex-info "" {}))
    (catch Exception e (println "Happens after exception"))
    (finally (println "Happens last no matter what")))
  )

(Or more realistically, see this comment from ptaoussanis.)

It'd be nice to have a helper to assert this behavior with rct, something like:

^:rct/test
(comment
  (with-printlns
    (try
      (println "Happens first")
      (throw (ex-info "" {}))
      (catch Exception e (println "Happens after exception"))
      (finally (println "Happens last no matter what"))))
  ;=>> ["Happens first" 
  ;     "Happens after exception" 
  ;     "Happens last no matter what"]
  )

I want something different than with-out-str because (1) I want it to still print, and (2) sometimes weird binding conveyance stuff happens with with-out-str.

E.g. using the promesa library:

(with-out-str
  (let [p (-> (p/future (Thread/sleep 50) (println "Future"))
              (p/handle (fn [_ __] (println "Finally"))))]
    (println "Built")
    @p))

; Finally
;=> "Built\nFuture\n"

The "Finally" is printed and the rest is captured by with-out-str.

[matthewdowney]

The downside would be that if this goes in a util namespace or something, anyone who wants to use it would want to depend on rct within the codebase under test.

But it would be optional, so no forced dependency.