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Metaprogramming in Elixir

Unit Tests

Explore methods to unit test complex macros in Elixir, focusing on converting abstract syntax trees to source strings for validation. Learn when to apply unit tests and why integration testing is often preferable for macro code generation. This lesson helps you gain confidence in testing recursive macros and ensuring your metaprogramming code is reliable and maintainable.

We'll cover the following...

We should use unit-testing macros only for cases where we need to test a tricky code generation in isolation. Over-testing macros at the unit level can lead to brittle tests because we can only test the AST generated from the macro or the string of source produced. These values can be hard to match against and are subject to change, leading to error-prone tests that are difficult to maintain.

The project

Experiment with the following widget. Edit and test the code as guided in the lesson.

ExUnit.start
Code.require_file("translator.exs", __DIR__)

defmodule TranslatorTest do
  use ExUnit.Case

  defmodule I18n do
    use Translator

    locale "en", [
      foo: "bar",
      flash: [
        notice: [
          alert: "Alert!",
          hello: "hello %{first} %{last}!",
        ]
      ],
      users: [
        title: "Users",
        profile: [
          title: "Profiles",
        ]
    ]]

    locale "fr", [
      flash: [
        notice: [
          hello: "salut %{first} %{last}!"
        ]
    ]]
  end


  test "it recursively walks translations tree" do
    assert I18n.t("en", "users.title") == "Users"
    assert I18n.t("en", "users.profile.title") == "Profiles"
  end

  test "it handles translations at root level" do
    assert I18n.t("en", "foo") == "bar"
  end

end
The `TranslatorTest ` module with unit tests

Let’s add unit tests to our ...