Rails Minitest model method test

Question

I've got User model method which calculate a number of user membership. I want to it test by MiniTest. Here is what I have:

  def member_for
    time_diff = Time.current - created_at
    result = ActiveSupport::Duration.build(time_diff.to_i).parts
    return "Member for #{result[:years]}y, #{result[:months]}m" if result.key?(:years) && result.key?(:months)

    if result.key?(:years) && result.key?(:days)
      "Member for #{result[:years]}y, #{result[:days]}d"
    elsif result.key?(:months)
      "Member for #{result[:months]}m"
    elsif result.key?(:days)
      "Member for #{result[:days]}d"
    end
  end

I was trying to write some MiniTest:

  test 'member for' do
    user.created_at = 2.years.ago + 3.months + 2.days
    user.member_for
  end

  private

  def user
    @user ||= users(:one)
  end

But to be honest, I don't know how to compare if it returns the correct string.

Answer 1

You can decrease the cyclic complexity as well as removing several bugs which give the wrong duration (by omitting weeks and months) by simply iterating across the parts:

  def member_for
    time_diff = Time.current - created_at
    parts = ActiveSupport::Duration.build(time_diff.to_i).parts
    formatted = parts.except(:seconds).map do |unit, value|
      "#{value} #{unit}"
    end
    "Member for #{formatted.to_sentance}"     
  end

You can use a simple lookup table or the I18n API if you want to have abbreviations instead of the full unit names. Array#to_sentance is from ActiveSupport.

You would then test this by:

class MemberTest < ActiveSupport::TestCase
  test 'member_for without weeks' do
    user.created_at = 2.years.ago + 3.months + 2.days
    assert_equal(user.member_for, 'Member for 1 year, 3 months and 2 days')
  end

  test 'member_for with weeks' do
    user.created_at = 2.years.ago + 2.weeks
    assert_equal(user.member_for, 'Member for 1 year and 2 weeks')
  end

  private

  def user
    @user ||= users(:one)
  end
end

However its questionable if this code really belongs in a model in the first place since its presentation and not buisness logic. I would say a helper or decorator/presenter is more suitible then cramming more logic into your models.