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Getting Started with expectations/clojure-test using ClojureScript

NOTE: ClojureScript support, via planck is coming in 2.0.0 but you can try it out now via the develop branch in the repo!

You can use expectations/clojure-test to run tests in both Clojure and ClojureScript. Many tests will work without changes in both Clojure and ClojureScript, though of course some will require changes for the different environments. This section describes how to use expectations/clojure-test in ClojureScript and the differences from using it in Clojure -- see the other sections for details of how to use it in Clojure for a complete picture.

Installation

In order to run expectations/clojure-test with ClojureScript, you will use olical/cljs-test-runner and the Clojure tool clj.

Your deps.edn should include this information:

{:aliases {:cljs-runner
             {:extra-deps {com.github.seancorfield/expectations {:mvn/version "2.1.201"},
                           olical/cljs-test-runner {:mvn/version "3.8.1"},
                           pjstadig/humane-test-output {:mvn/version "0.11.0"}},
              :extra-paths ["src" "test" "cljs-test-runner-out/gen"],
              :main-opts ["-m" "cljs-test-runner.main"
                          "--doo-opts" "dooopts.edn"
                          "-x" "planck"]}}}

You will need two small .edn files in your project:

dooopts.edn:

{:paths {:planck "planck --compile-opts planckopts.edn"}}

planckopts.edn:

{:warnings {:private-var-access false}}

To run the tests, you run:

clj -M:cljs-runner

These tests will take a good while longer to run than the same tests in Clojure, so if you don't get any output for a while, that is not necessarily a bad thing.

Requirements

The ClojureScript version of expectations/clojure-test works (at present) only with a specific implementation of self-hosted ClojureScript: planck. You will have to install planck yourself in order to use expectations/clojure-test with ClojureScript.

You will have to get planck -h to work locally. See here for instructions on how to install planck on a variety of systems. Planck 2.24.0 or later is required.

Humane Test Output

The use of Paul Stadig's Humane Test Output, is optional for the Clojure version of expectations/clojure-test but it is required for the ClojureScript version of expectations/clojure-test.

The Basics

This example is the ClojureScript version of the quick comparison provided for the Clojure version of expectations/clojure-test, and provides a quick comparison with clojure.test (the tests match those in the clojure.test documentation):

(require '[expectations.clojure.test :refer [defexpect expect expecting]])

(defexpect simple-test                  ; (deftest simple-test
  (expect 4 (+ 2 2))                    ;   (is (= 4 (+ 2 2)))
  (expect number? 256)                     ;   (is (instance? Long 256))
  (expect (.startsWith "abcde" "ab"))   ;   (is (.startsWith "abcde" "ab"))
  (expect ##Inf (/ 1 0))                ;   (is (thrown? ArithmeticException (/ 1 0)))
  (expecting "Arithmetic"               ;   (testing "Arithmetic"
    (expecting "with positive integers" ;     (testing "with positive integers"
      (expect 5 (+ 2 2))                ;       (is (= 4 (+ 2 2)))
      (expect 7 (+ 3 4)))               ;       (is (= 7 (+ 3 4))))
    (expecting "with negative integers" ;     (testing "with negative integers"
      (expect -4 (+ -2 -2))             ;       (is (= -4 (+ -2 -2)))
      (expect -1 (+ 3 -4)))))           ;       (is (= -1 (+ 3 -4))))))

The third example could also be written as follows, since expect allows an arbitrary predicate in the "expected" position:

  (expect #(.startsWith % "ab") "abcde")

Or like this, since expect allows a regular expression in the "expected" position:

  (expect #"^ab" "abcde")

Both of these more accurately reflect an expectation on the actual value "abcde", that the string begins with "ab", than the is equivalent which has the actual value embedded in the test expression. Separating the "expectation" (value or predicate) from the "actual" expression being tested often makes the test much clearer.

Differences from the Clojure version of expectations/clojure-test

Here is the list of features from Expectations supported by the Clojure version of expectations.clojure.test where there are differences in the ClojureScript implementation.

* Class test

Classes are all different in ClojureScript, and in some cases things that would be a class in Clojure are different in ClojureScript. For instance, lists are a class:

(defexpect class-test cljs.core/List '(a b c))

and this test passes. Strings, however, don't have an easily discoverable type or class, and are better handled with a predicate:

(defexpect string-class-test string? "abc")

In general, the classes in ClojureScript will not be the same as the classes in Clojure. You can do this to write a test that will work in both environments:

(defexpect both-class-test (expect (= (type "abc") (type "def"))))

but you cannot write this:

(defexpect bad-both-class-test (type "abc") (type "def"))

because (type "abc") yields something that tests positive as a fn?, causing expectations to think it is a predicate. Which, as it happens, it is not.

* Exception test

Exceptions are very different in ClojureScript from Clojure.

The Clojure example:

(defexpect divide-by-zero ArithmeticException (/ 12 0))

doesn't even throw an exception -- it returns ##Inf. You can do this for that situation:

(defexpect divide-by-zero ##Inf (/ 12 0))

but be careful putting ##Inf in a reader conditional, as some versions of Clojure don't handle that well. But all of this is a bit off-topic, as we are discussing exceptions.

Exceptions certainly exist and can be thrown. You can throw pretty much anything in Javascript. There is no Throwable class in Clojurecript to distinguish things that can be thrown from anything else. The only exception supported in expectations/clojure-test in ClojureScript is where the exception is: js/Error. For example:

(defexpect exception js/Error (count 5))

will pass, because (count 5) throws js/Error.

* with-test

There is no with-test in cljs.test, so it is not available in expectations/clojure-test.

* Specs

Specs are always supported, and work equivalently to Clojure.

Useful Additional Information

The end of the Clojure Getting Started provides additional information on how to use expectations/clojure-test, and most of the information is directly applicable to using expectations/clojure-test in ClojureScript as well.

Further Reading

Expectations provides a lot more: