Elvis Test

elvis_test.exs

defmodule ElvisTest do
  use ExUnit.Case

  def a ~> b, do: elvis(a, b)

  def elvis(nil, fun), do: nil

  def elvis({nil, default_val}, fun), do: elvis(default_val, fun)

  def elvis(val, fun), do: fun.(val)

  test "example" do
    tag = fn inner, tag -> "<#{tag}>#{inner}</#{tag}>" end

    params = %{title: "Movie Title", description: "Great Movie A+"}

    result_1 =
      params[:description]
      ~> fn a -> tag.(a, "h1") end
      ~> fn a -> tag.(a, "div") end

    assert "<div><h1>Great Movie A+</h1></div>" == result_1

    result_2 =
      params[:sub_title]
      ~> fn a -> tag.(a, "h1") end
      ~> fn a -> tag.(a, "div") end

    refute result_2

    result_2 =
      {params[:sub_title], "No Subtitle"}
      ~> fn a -> tag.(a, "h1") end
      ~> fn a -> tag.(a, "div") end

    assert "<div><h1>No Subtitle</div>" == result_1

  end
end