Elixir’s built in testing library is called ExUnit. It’s a proper testing
framework, which, although simple, gives the developers a lot of power and
flexibility. If you come from Ruby land, I am sure you’ve been in a position
where you want to set a certain test to be skipped. For example, RSpec in Ruby
does it with the
pending method. Let’s see how we can customize our test
suite so ExUnit can skip over tests in our test suite.
ExUnit comes with this neat feature called tags. Tags are basically module variables in the test module. In the context of the test, you can think of them as annotations. So, by tagging a test, the value of the tag can be used in the test itself, by passing the context.
defmodule FileTest do # Changing directory cannot be async use ExUnit.Case, async: false setup context do # Read the :cd tag value if cd = context[:cd] do prev_cd = File.cwd! File.cd!(cd) on_exit fn -> File.cd!(prev_cd) end end :ok end @tag cd: "fixtures" test "reads utf-8 fixtures" do File.read("hello") end end
Now, how can we utilize tags to get RSpec’s
pending funcionality in ExUnit?
Running tests by tag
Running tests by tag is really simple in ExUnit. Basically, ExUnit has the ability to skip/include any test by it’s tag.
For example, let’s say you have tagged couple of tests that are brittle:
defmodule SomeTest do use ExUnit.Case, async: false @tag :brittle test "some brittle code" do # test here... end end
Now, you can run only the tests with the
brittle tag, by executing:
mix test test/some_test.exs --include brittle
Having this in mind, let’s introduce a custom tag of ours so we can make our
Although the word “custom” used in programming often means something complicated done from scracth by the programmer, in this case it’s very simple.
Let’s take any test and tag it with
defmodule SomeTest do use ExUnit.Case, async: false @tag :pending test "always true" do assert 1 == 1 end end
We can exclude this “pending” test by executing our test suite with:
mix test --exclude pending
This will skip any tests that have the
:pending tag. Simple as that, we have
pending functionality just by excluding a tag. If you are wondering
if we can make the exclusion of the tag automatic - yes we can. In your
test_helper.exs add this line, before the
ExUnit.configure(exclude: [pending: true])
This configuration will tell ExUnit that it should always skip tests that are
:pending. Now, every time you run your tests, the tests tagged with
:pending will be excluded.
Do you have any other interesting configuration trick in your ExUnit suite? Feel free to share them in the comments, I would love to learn more about ExUnit!
Thanks for reading!
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