CODEWITHSUNDEEP
clojure
Neoasimov
Neoasimov

Reputation: 1111

Clojure: how to know if a function (test-vars) printed something to *out*?

I am looking for a way to determine if a function printed (using println or anything similar).

What I am trying to determine is if test-vars printed something or not.

The issue with this function is that it doesn't return anything, but only print things when errors got issues, but I want to know if it succeeded or not and the only way I see to know it is to check if it printed something or not.

Even better would be a way to "intercept" what is going to out and to put it in a variable.

After the comments from @lee and @leetwinski I tried the following:

(deftest test-1
  (testing
  (is (= 1 2))))

Then I tried to run that test using:

(let [printed (with-out-str (test-vars [#'test-1]))]
    (print (str "Printed size: " (count printed))))

But here is what I got:

FAIL in (test-1) (form-init505699766276988020.clj:103)
expected: (= 1 2)
  actual: (not (= 1 2))
Printed size: 0
nil

So, what test-vars outputs has been outputted anyway. Then printed was empty.

Upvotes: 1

Views: 595

Answers (2)

leetwinski
leetwinski

Reputation: 17859

in addition to @Lee's answer: in general you could just rebind *out* to any other writer you want:

temporary binding:

user> (binding [*out* (java.io.StringWriter.)]
        (println 101)
        (str *out*))
"101\n"

is just an analogue to with-out-str

thread-local binding:

user> (set! *out* (java.io.StringWriter.))
#object[java.io.StringWriter 0x575e6773 ""]

user> (println 123)
nil

user> (str *out*)
"123\n"

here we rebind the *out*, for the current thread (and for all the threads, spawned from it, AFAIK).

Upvotes: 1

Lee
Lee

Reputation: 144136

You can use with-out-str which intercepts printed values and collects them into a string:

(let [printed (with-out-str (test-vars))]
    ...)

Upvotes: 1

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