Unit Testing in Clojure

One thing I love about Clojure is the built in unit tests. Unit tests are great for making sure your code does what it needs to do and introducing new features or bug fixes doesn't break anything. You can refactor your code anytime you want and be sure that you did not break anything. Unit tests also serve as a living documentation for your code base, newcomers can look at the code base and get basic understanding of how your API works.

Clojure's core library includes a test framework written by Stuart Sierra. If there is anything that is not covered here the best place to look for it is the source code itself.

Testing framework is under the namespace clojure.test, 

(ns your-test-namespace
  (:use clojure.test))

is all thats needed to load the framework. Assuming we would like to test the following function, 

(defn add2 [x] 
  (+ x 2))

There are two ways to define tests, you can either define your tests with the function itself, 

(with-test
  (defn add2 [x] 
    (+ x 2))
  (is (= 4 (add2 2)))
  (is (= 5 (add2 3))))

but I believe that just bloats the code base, or you can define your tests separately using the deftest macro, 

(deftest test-adder
  (is (= 24  (add2 22))))

Tests can also be grouped together, 

(deftest arithmetic
  (addition)
  (subtraction))

For testing private functions, you need to use the following macro (courtesy of chouser), 

(defmacro with-private-fns [[ns fns] & tests]
  "Refers private fns from ns and runs tests in context."
  `(let ~(reduce #(conj %1 %2 `(ns-resolve '~ns '~%2)) [] fns)
     ~@tests))

then wrap your tests with with-private-fns, 

(with-private-fns [org.foo.bar [fn1 fn2]]
  (deftest test-fn1..)
  (deftest test-fn2..))

If you need to run code before and after tests, to set up the context in which tests should be run. Define a fixture which is just a function that calls another function passed as an argument. 

(defn my-fixture [f]
  ;;Perform setup, establish bindings, whatever.
  (f)  ;;Then call the function we were passed.
  ;;Tear-down / clean-up code here.
 )

Fixtures are run repeatedly, once for each test, they can be attached to the current namespace like this, 

(use-fixtures :each fixture1 fixture2 ...)

You can also have a fixture that only runs once, around all the tests in the namespace. 

(use-fixtures :once fixture1 fixture2 ...)

To run the tests you defined from REPL you can use, 

(run-tests)

With out a namespace run-tests will run the tests defined in the namespace you are in, you can pass it namespaces to run tests defined in other namespaces as well. 

(run-tests 'your.namespace 'some.other.namespace)

If you want to run all tests in all namespaces, 

(run-all-tests)

Or use leiningen, 

lein test
Tags: clojure unit-testing