Testing Elixir

July 30, 2012

When learning a new linage, one of the first steps one needs to take is learning its testing frameworks. Elixir being a relatively new language, it only has one ExUnit. In this blog post, I’ll walk you through writing your first tests.

First thing to note are that Elixir tests are written in .exs files, not the standard .ex Elixir file format. .exs files are written in the Elixir language, but are never compiled only ever interpreted.

Now lets jump into some code. First lets create a test helper.

$ mkdir test
$ touch test/test_helper.exs

### Inside test_helper.exs

ExUnit.start []

Thats all we need to get started. We can later put utility methods in here, if they’re needed. Now lets write a testing module.

### Inside adder_test.exs

Code.require_file "../test_helper", __FILE__

defmodule Adder.Test do
  use ExUnit.Case, async: true
end

Here we do a few things. Require the test_helper file we just wrote, create the module we will fill with tests, and import the ExUnit.Case methods. One thing to note here is the async option on ExUnit.Case. When set to true, all the of the tests will run in parallel. Whenever possible set this to true. Lets write a test.

test "adds one and one correctly" do
  assert 2 == 1 + 1
end

Like many other languages ExUnit uses the standard assert clauses, but wraps them in a test block. We can run this test with the command elixir test/adder_test.exs. If everything was written correctly you should see:

.

1 test, 0 failures.

Woot! We ran our first Elixir test. Now lets stream line the process with a shell script.

# Inside tester.sh

elixir -r "lib/**/*.ex" -r "test/test_helper.exs" -pr "test/**/*_test.exs"

This script will load every .ex file in your lib directory, then require the test helper, and then load each test file sequentially.

Thats it. Now just sh tester.sh to run all your tests. Have fun!