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clojurescript.test Build Status


I strongly suggest migrating to use the official core cljs.test + for test-runners and leiningen/boot integration. Thanks to all contributors for helping make testing ClojureScript workable until those tools arrived/matured!

A maximal port of clojure.test to ClojureScript.


I want to be able to write portable tests to go along with my portable Clojure[Script], and clojure.test's model is Good Enough™ (it's better than that, actually). Combine with something like cljx to make your ClojureScripting a whole lot more pleasant.


clojurescript.test is available in Maven Central. Add it to your :plugins in your Leiningen project.clj:

[com.cemerick/clojurescript.test "0.3.3"]

(clojurescript.test is actually a project dependency and a Leiningen plugin; adding it as the latter just helps simplify test configuration, as you see below.)

Or, add this to your Maven project's pom.xml:



clojurescript.test provides roughly the same API as clojure.test, thus making writing portable tests possible.

(Note that clojurescript.test doesn't take any responsibility for any hosty or otherwise-unportable things you do in your tests, e.g. js/... or naming JVM types or Clojure- or ClojureScript-only functions; either don't do that, or use something like cljx to include both Clojure and ClojureScript code in the same file.)

Here's a simple ClojureScript namespace that uses clojurescript.test:

(ns cemerick.cljs.test.example
  (:require-macros [cemerick.cljs.test
                    :refer (is deftest with-test run-tests testing test-var)])
  (:require [cemerick.cljs.test :as t]))

(deftest somewhat-less-wat
  (is (= "{}[]" (+ {} []))))

(deftest javascript-allows-div0
  (is (= js/Infinity (/ 1 0) (/ (int 1) (int 0)))))

  (defn pennies->dollar-string
    {:pre [(integer? pennies)]}
    (str "$" (int (/ pennies 100)) "." (mod pennies 100)))
  (testing "assertions are nice"
    (is (thrown-with-msg? js/Error #"integer?" (pennies->dollar-string 564.2)))))

Note: each test namespace in your project must (:require cemerick.cljs.test) even if you only use macros. Otherwise, the ClojureScript compilation process won't include clojurescript.test in its output, resulting in an error similar to "ReferenceError: Can't find variable: cemerick".

You can load this into a ClojureScript REPL, and run its tests using familiar functions:

=> (t/test-ns 'cemerick.cljs.test.example)

Testing cemerick.cljs.test.example
{:fail 0, :pass 3, :test 3, :error 0}

=> (test-var #'cemerick.cljs.test.example/somewhat-less-wat)
{:fail 0, :pass 1, :test 1, :error 0}

All of the test-definition macros (deftest and with-test, as well as the set-test utility) add to a global registry of available tests (necessary given ClojureScript's lack of namespaces), so you can also define, redefine, and run tests interactively:

=> (deftest dumb-test
     (is (empty? (filter even? (range 20)))))
#<[object Object]>
=> (t/test-ns 'cemerick.cljs.test.example)

Testing cemerick.cljs.test.example

FAIL in (dumb-test) (:0)
expected: (empty? (filter even? (range 20)))
  actual: (not (empty? (0 2 4 6 8 10 12 14 16 18)))
{:fail 1, :pass 3, :test 4, :error 0}

Writing portable tests

Because clojurescript.test has (approximately) the same API as clojure.test, writing portable tests with it is easy. For example, the test namespace above can be made portable using cljx like so:

(ns cemerick.cljs.test.example
  #+clj (:require [clojure.test :as t
                   :refer (is deftest with-test run-tests testing)])
  #+cljs (:require-macros [cemerick.cljs.test
                           :refer (is deftest with-test run-tests testing test-var)])
  #+cljs (:require [cemerick.cljs.test :as t]))

(deftest somewhat-less-wat
  (is (= "{}[]" (+ {} []))))

(deftest javascript-allows-div0
  (is (= js/Infinity (/ 1 0) (/ (int 1) (int 0)))))

  (defn pennies->dollar-string
    {:pre [(integer? pennies)]}
    (str "$" (int (/ pennies 100)) "." (mod pennies 100)))
  (testing "assertions are nice"
    (is (thrown-with-msg? #+cljs js/Error #+clj Error #"integer?"
          (pennies->dollar-string 564.2)))))

Note that test-var is a macro in clojurescript.test; this allows you to portably write code like (test-var #'name-of-test), even though ClojureScript doesn't support #' or the (var ...) special form. test-var forms macroexpand to calls to cemerick.cljs.test/test-function, which is the corollary to clojure.test's test-var.

Using with lein-cljsbuild

Most people use lein-cljsbuild to automate their ClojureScript builds. Using clojurescript.test within that context is easy. Here is an excerpt of the lein-cljsbuild configuration that this project uses to run its own clojurescript.test tests (look in the project.clj file for examples using phantomjs, slimerjs, node, and rhino):

:plugins [[lein-cljsbuild "1.0.0"]
          [com.cemerick/clojurescript.test "0.2.3"]]
:cljsbuild {:builds [{:source-paths ["src" "test"]
                      :compiler {:output-to "target/cljs/testable.js"
                                 :optimizations :whitespace
                                 :pretty-print true}}]
            :test-commands {"unit-tests" ["phantomjs" :runner

(Note that the extra_command_file.js reference and literal_js_was_evaluated expression are examples, and not necessary for your usage. Please continue reading below.)

Everything here is fairly basic, except for the :test-commands entries, which describes the shell command that will be executed when lein-cljsbuild's test phase is invoked (either via lein cljsbuild test, or just lein test because its hook is registered). In this case, it's going to run phantomjs, passing as arguments:

  1. The path to the clojurescript.test test runner script (denoted by :runner, which I'll explain momentarily…), and
  2. Either paths to ClojureScript compiler output (a lein-cljsbuild :output-to value defined elsewhere in the project.clj), or paths to other arbitrary JavaScript files (useful for injecting external libraries, polyfills, etc), or arbitrary JavaScript expressions (useful for e.g. configuring runtime test properties...see the subsection below on using this capability, especially in conjunction with advanced compilation).

clojurescript.test bundles test runner scripts for various environments (currently, phantomjs and slimerjs, node.js, and rhino). As long as you add clojurescript.test to your project.clj as a :plugin, then it will replace any occurrences of :runner, :node-runner and :rhino-runner in your :test-commands vectors with the path to the corresponding test runner script.

Outside of the :test-commands vector in your :cljsbuild configuration, clojurescript.test will replace namespaced corollaries to these test runner keywords (:cljs.test/runner, :cljs.test/node-runner, and :cljs.test/rhino-runner). This allows you to have paths to clojurescript.test runner scripts injected anywhere into your project.clj you like.

SlimerJS and PhantomJS

Though the :runner test runner is compatible with both of these scriptable browser environments, SlimerJS is currently recommended because:

  • It can use effectively any version of Firefox / XULRunner (PhantomJS has been stuck on a very old version of webkit for years now), and so effectively all of the "modern" browser/web platform APIs are available to test.
  • It is reasonably fast (faster than phantomjs, though still ~40% slower than node)
  • It can easily be run headlessly, via xvfb

In general, you should download and use the latest "lightweight" slimerjs build.

Check out the SlimerJS :test-commands in project.clj for examples of how to best use xvfb and slimerjs together, and look at .travis.yml for an example of how to arrange your TravisCI configuration such that both of these tools are available there (analogous configuration can be applied in any other CI or automated environment of your choice).


To run your tests with node.js instead of phantomjs, just change the executable name and the :runner keyword in your :test-commands vectors like so:

:test-commands {"unit-tests" ["node" :node-runner
                              ; extra code/files here...

Note that you must compile your ClojureScript code with :advanced or :simple `:optimizations to run it on node.js.


To run your tests with rhino, change the executable name and the :runner keyword in your :test-commands vectors like so:

:test-commands {"unit-tests" ["rhino" "-opt" "-1" :rhino-runner
                              ; extra code/files here...

Note that rhino doesn't support any HTML or DOM related functions and objects so it can be used mainly for business-only logic or you have to mock all DOM functions by yourself.

All test runner scripts load the output of the ClojureScript compilation, run all of the tests found therein, reports on them, and fails the build if necessary.

clojurescript.test supports all of Google Closure's compilation modes, including :advanced, but it does NOT support :none cljsbuild optimization option.

Configuring tests via JavaScript files/expressions in :test-commands

As noted above, you can have arbitrary JavaScript files and/or expressions loaded before or after your compiled ClojureScript. One of the most useful aspects of this is that you can configure properties of your tests; for example, when using double-check, you can control the number of iterations checked by each defspec test by setting a Java system property. While JavaScript doesn't have a corollary of system properties, you can add a JavaScript expression to your :test-commands vector(s) that sets a property on some globally-accessible object, e.g.:

:test-commands {"rigorous" ["phantomjs" :runner

Then, in your ClojureScript test file(s), you can look up this dynamically-set value, using a default if it's not set:

(def iteration-count (or (this-as this (aget this "defspec_iters")) 1000))

The use of aget and a string property lookup is necessary to ensure that the property name will not be renamed/obfuscated by Google Closure when run with :advanced optimizations. Prior examples of this practice touched window, but that name is undefined in node.js; using this when setting and looking up the test configuration value makes it so that the same code (and configuration) can be used in any test environment.

Asynchronous testing

Problem: various operations in JavaScript are necessarily asynchronous, from things as simple as DOM event callbacks to more involved activity like querying or modifying IndexedDB databases or interacting with core.async channels. This means that the testing "context" may have moved on (and your JavaScript environment's execution may have completed entirely) before your callbacks/go blocks/etc have fired/completed…a big problem if those asynchronous constructs contained assertions.

Starting with version 0.3.0, clojurescript.test provides ways to explicitly control when each test is complete.

First, an example of a test that will not perform the intended (asynchronous) assertion:

(ns async-example
  (:require-macros [cemerick.cljs.test :refer (is deftest)])
  (:require [cemerick.cljs.test :as t]))
(deftest timeout
  (let [now #(.getTime (js/Date.))
        t (now)]
	  (fn [] (is (>= (now) (+ t 2000))))

In the best case, the is assertion's results will be attributed to some other test; in the worst case, the JavaScript environment will have exited before the setTimeout callback is scheduled to be invoked, and the asynchronous assertion will never be run at all.

Modifying this example as follows will yield useful/correct behaviour:

  1. Add ^:async metadata to the deftest name.
  2. You must call (done) using the asynchronous deftest's testing context in order for that test to finish, and cause the next test in the current run to start.
(ns async-example
  (:require-macros [cemerick.cljs.test :refer (is deftest done)])
  (:require [cemerick.cljs.test :as t]))

(deftest ^:async timeout
  (let [now #(.getTime (js/Date.))
        t (now)]
	  (fn []
	    (is (>= (now) (+ t 2000)))

Compared to the first example:

  1. This test will be run after any synchronous tests in the same namespace that are included in the current test run.
  2. Control exiting the lexical scope of deftest will have no effect upon the wider test run (compared to synchronous tests, the "completion" of which cause the next test in a run to be started).
  3. When the setTimeout callback is invoked, the assertion therein will be run, and properly attributed to the timeout test.
  4. The (done) call will close the timeout test context, and start the next test in the run.

Note that you have complete control over when a test is done; the setTimeout callback above could just as well spin off another setTimeout call (or use any other callback-based API), or send or block on a core.async channel, etc.

If you don't explicitly close a test's context via (done), the clojurescript.test test runner will never move on to the next test, and your test run will be permanently stalled. You can unwedge yourself from this situation at the REPL in a couple of different ways, see "Canceling asynchronous tests".

The rest of this section will dig into the finer details of using the asynchronous testing facilities.

Test contexts

Each test defined by clojurescript.test carries its own test context. This is defined implicitly by deftest and other test-creation macros. The body of each test is also wrapped within a cemerick.cljs.test/with-test-ctx form. This macro does a couple of things:

  • It implicitly binds the test context provided to it to -test-ctx within its scope.
  • If the test context is asynchronous (i.e. the corresponding deftest was marked with ^:async metadata), then with-test-ctx will wrap any containing body of code with a try/catch form that will call (done) with any error thrown in the course of the body's execution. This ensures that the test context associated with an asynchronous test that fails with an exception is automatically closed, starting the next test.

The is assertion macro will pick up the anaphoric -test-ctx binding automatically when provided with one or two arguments (the form to evaluate/test, and an optional message). Alternatively, you can explicitly pass a test context to is.

Putting this all together allows you to define asynchronous tests that use common functions that contain asynchronous processing and/or assertions, passing the test context around explicitly in order to properly tie test results to the "source" tests. For example, here's the example from before, refactored to put the asynchronous call and assertion in a helper function:

(ns async-example
  (:require-macros [cemerick.cljs.test :refer (is deftest done with-test-ctx)])
  (:require [cemerick.cljs.test :as t]))

(defn- timeout-helper
  [test-context delay]
  (with-test-ctx test-context
    (let [now #(.getTime (js/Date.))
        t (now)]
	    (fn []
	      (is (>= (now) (+ t delay)))

(deftest ^:async timeout
  (timeout-helper 2000))

Because is and done are within with-test-ctx's lexical scope, they'll pick up the implicit test context binding automatically.

Alternatively, you could write timeout-helper like so, always passing the test context explicitly:

(defn- timeout-helper
  [test-context delay]
  (let [now #(.getTime (js/Date.))
        t (now)]
      (fn []
        (is test-context (>= (now) (+ t delay))
		  "an assertion message is required when explicitly passing test context to `is`")
        (done test-context))

A final variation is to establish the -test-ctx binding that is and done look for yourself:

(defn- timeout-helper
  [-test-ctx delay]
  (let [now #(.getTime (js/Date.))
        t (now)]
      (fn []
        (is (>= (now) (+ t delay)))

This is somewhat less verbose than other options, but necessitates very careful naming of -test-ctx (if you call done or done* without a test context, you'll have a bad time), and does not provide the asynchronous error-handling benefits of with-test-ctx.

Reporting errors

with-test-ctx will automatically catch and report errors that occur in asynchronous tests. However, if you're not using with-test-ctx, or want/need to catch certain errors manually, you can report them via the done macro (e.g. (done error)) if you are nevertheless within a with-test-ctx body, or via the done* function (e.g. (done* test-context error)). As with any other done invocation, this will close the test context and start the next test in the run.


You can use all of the facilities described here to test core.async code just as you would test callback-based APIs of all sorts. Under the covers, the asynchrony provided by core.async in ClojureScript is also mediated by callbacks, so all the same semantics apply: declare your tests to be asynchronous via the ^:async metadata, and be sure to call (done) one way or the other when each test's context should be closed.

Here's an example of core.async (and a profligate use of go blocks) used in conjunction with clojurescript.test, pulled from clojurescript.test's own test suite:

(deftest ^:async core-async-test
  (let [inputs (repeatedly 10000 #(go 1))]
    (go (is (= 10000 (<! (reduce
                           (fn [sum in]
                             (go (+ (<! sum) (<! in))))
Portably testing core.async code with clojurescript.test and clojure.test

Clojure's clojure.test does not provide any control over test lifecycle to accommodate assertions being performed in asynchronously-executed code paths, i.e. there is no done to call when we want a test to be considered complete. To work around this, clojurescript.test includes cemerick.cljs.test/block-or-done macro, which enables one to test code that uses the only Clojure/ClojureScript portable asynchrony option, core.async. In Clojure, block-or-done will block the completion of the enclosing clojure.test deftest until the provided channel is yields a value; in ClojureScript, block-or-done will call (done) when the provided channel yields a value.

This allows us to write the above core.async-using test in a portable way, that will work on either Clojure or ClojureScript:

(deftest ^:async pointless-counting
  (let [inputs (repeatedly 10000 #(go 1))
        complete (async/chan)]
    (go (is (= 10000 (<! (reduce
                           (fn [sum in]
                             (go (+ (<! sum) (<! in))))
        (>! complete true)) 
    (block-or-done complete)))

Canceling asynchronous tests

Every function or macro that starts a clojurescript.test test run (e.g. run-tests, test-ns, etc) will return a map of the test environment that summarizes the results of the synchronous tests included in that run. Within that environment's map is an :async entry, the value of which is an atom containing another test environment, dedicated to the asynchronous portion of the test run.

In ClojureScript

If you run a set of tests which appear to have wedged on the asynchronous portion (perhaps because one of your tests failed to close its testing context via (done) or (done* ...), or maybe a bug is causing a test run to carry on longer than desired), you can cancel the further processing of the test run by calling (cemerick.cljs.test/stop ...), passing the value of the :async slot of the top-level test environment described above. This will not cancel any outstanding asynchronous processing your tests have provoked in the JavaScript environment (e.g. callbacks, pending core.async puts or takes, etc), but it will stop the test run corresponding to the test environment from continuing if and when the wedged asynchronous test does close its testing context.

In Clojure

Assuming your asynchronous tests are using block-or-done (discussed above), test running functions and macros will block until all tests are complete. If you suspect those tests will not complete, the only solution to this is to interrupt the blocked REPL evaluation, supported by various nREPL clients and tools.


  • Bug: filenames and line numbers are not currently reported properly.

Differences from clojure.test

TODO the differences noted here are out of date, and do not account for the additional differences (esp. w.r.t. the test runtime maintenance bits) introduced by supporting asynchronous testing starting in 0.3.0.

  • docstrings bear little to no semblence to the library's actual operation
  • Namespace test hooks must be defined using the deftesthook macro


  • *report-counters* is now bound to an atom, not a ref
  • *testing-vars* now holds symbols naming the top-levels under test, not vars
  • *test-out* is replaced by *test-print-fn*, which defaults to nil, and is only bound to cljs.core/*print-fn* if it is bound to a non-nil value.
  • run-tests is now a macro; run-tests* does the same, but does not offer a no-arg arity
  • use-fixtures is now a macro, and there is no underlying multimethod to extend as in clojure.test.


  • Stack traces from caught exceptions are obtained via Error.stack, which appears to only be supported in Chrome, FF, Safari, and IE 10+. The value of Error.stack in Rhino (at least, the version specified for use by ClojureScript) is always an empty string; other JavaScript environments may be similar.
  • File and line numbers of reported exception failures may be missing in JavaScript environments that do not support the lineNumber or fileName properties of Error.


  • *load-tests* is now private, and will probably be removed. The use case for Clojure (which is rarely taken advantage of AFAICT) seems irrelevant for ClojureScript; if you do or don't want tests in production, you just change your cljsc/lein-cljsbuild configuration.
  • file-position was already deprecated and unused
  • Not applicable
  • get-possibly-unbound-var
  • function?
  • *stack-trace-depth*

Need Help?

Send a message to the ClojureScript mailing list, or ping cemerick on freenode irc or twitter if you have questions or would like to contribute patches.


Copyright © 2013-* Chas Emerick and other contributors. Known contributors to clojure.test (which was the initial raw ingredient for this project) at the time of this project's inception were:

  • Stuart Sierra
  • Rich Hickey
  • Stuart Halloway
  • Phil Hagelberg
  • Tassilo Horn
  • Mike Hinchey

Distributed under the Eclipse Public License, the same as Clojure.


A maximal port of `clojure.test` to ClojureScript. DEPRECATED



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