Power Assert

Power Assert makes test results easier to understand, without changing your ExUnit test code.

Example test is here:

test "Enum.at should return the element at the given index" do
  array = [1, 2, 3, 4, 5, 6]; index = 2; two = 2
  assert array |> Enum.at(index) == two
end

Here is the difference between ExUnit and Power Assert results:

Enjoy 💪 !

Installation

Add Power Assert to your mix.exs dependencies:

defp deps do
  [{:power_assert, "~> 0.1.2", only: :test}]
end

and fetch $ mix deps.get.

Usage

Replace use ExUnit.Case into use PowerAssert in your test code:

## before(ExUnit)
defmodule YourAwesomeTest do
  use ExUnit.Case  # <-- **HERE**
end

## after(PowerAssert)
defmodule YourAwesomeTest do
  use PowerAssert  # <-- **REPLACED**
end

Done! You can run $ mix test.

Use with ExUnit.CaseTemplate

Insert use PowerAssert with ExUnit.CaseTemplate.using/2 macro:

## before(ExUnit.CaseTemplate)
defmodule YourAwesomeTest do
  use ExUnit.CaseTemplate
end

## after(PowerAssert)
defmodule YourAwesomeTest do
  use ExUnit.CaseTemplate

  # add the following
  using do
    quote do
      use PowerAssert
    end
  end
end

protip: useful command to replace use ExUnit.Case

$ git grep -l 'use ExUnit\.Case' | xargs sed -i.bak -e 's/use ExUnit\.Case/use PowerAssert/g'

How to use with other framework depending on ExUnit such as ExSpec or ShouldI

ExSpec

Append use PowerAssert after use ExSpec:

defmodule ExSpecBasedTest do
  use ExSpec
  use PowerAssert   # <-- append

  describe "describe" do
    it "it" do
      assert something == "hoge"
    end
  end
end

See also: test/ex_spec/ex_spec_test.exs

ShouldI

Append use PowerAssert after use ShouldI:

defmodule ShouldTest do
  use ShouldI
  use PowerAssert   # <-- append

  should "inside should" do
    assert something == "hoge"
  end
end

See also: test/should/should_test.exs

API

Only provide assert macro:

assert(expression, message \\ nil)

Dependencies

• ExUnit

Limitation

• NOT SUPPORTED
  • match expression ex: assert List.first(x = [false])
  • fn expression ex: assert fn(x) -> x == 1 end.(2)
  • :: expression ex: << x :: bitstring >>
    • this means string interpolations also unsupported ex: "#{x} hoge"
  • sigil expression ex: ~w(hoge fuga)
  • quote arguments ex: assert quote(@opts, do: :hoge)
  • case expression
  • get_and_update_in/2, put_in/2, update_in/2, for/1
  • <<>> expression includes attributes <<@x, "y">>; <<x :: binary, "y">>
  • __MODULE__.Foo
  • many macros maybe caught error...

Resources

• Testing with Power Assert in Elixir projects
• Power Assert Inside in Elixir

Author

Takayuki Matsubara (@ma2ge on twitter)

License

Distributed under the Apache 2 License.

Check LICENSE files for more information.