grade_school.rb

class School

  def to_hash
    school.sort.to_h
  end

  def add name, grade
    if school[grade]
      (school[grade] << name).sort!
    else
      school.store(grade, [name])
    end
  end

  def grade n
    school[n] ? school[n] : []
  end

  private

  attr_accessor :school

  def initialize
    self.school = {}
  end

end


#!/usr/bin/env ruby
gem 'minitest', '>= 5.0.0'
require 'minitest/autorun'
require_relative 'grade_school'
require 'pry'

class SchoolTest < Minitest::Test
  attr_reader :school

  def setup
    @school = School.new
  end

  def test_an_empty_school
    assert_equal({}, school.to_hash)
  end

  def test_add_student
    school.add('Aimee', 2)
    assert_equal({ 2 => ['Aimee'] }, school.to_hash)
  end

  def test_add_more_students_in_same_class
    school.add('Blair', 2)
    school.add('James', 2)
    school.add('Paul', 2)
    assert_equal({ 2 => %w(Blair James Paul) }, school.to_hash)
  end

  def test_add_students_to_different_grades
    school.add('Chelsea', 3)
    school.add('Logan', 7)
    assert_equal({ 3 => ['Chelsea'], 7 => ['Logan'] }, school.to_hash)
  end

  def test_get_students_in_a_grade
    school.add('Bradley', 5)
    school.add('Franklin', 5)
    school.add('Jeff', 1)
    assert_equal %w(Bradley Franklin), school.grade(5)
  end

  def test_get_students_sorted_in_a_grade
    school.add('Franklin', 5)
    school.add('Bradley', 5)
    school.add('Jeff', 1)
    assert_equal %w(Bradley Franklin), school.grade(5)
  end

  def test_get_students_in_a_non_existant_grade
    assert_equal [], school.grade(1)
  end

  def test_sort_school # rubocop:disable Metrics/MethodLength
    [
      ['Jennifer', 4], ['Kareem', 6],
      ['Christopher', 4], ['Kyle', 3]
    ].each do |name, grade|
      school.add(name, grade)
    end
    sorted = {
      3 => ['Kyle'],
      4 => %w(Christopher Jennifer),
      6 => ['Kareem'],
    }
    assert_equal sorted, school.to_hash
    assert_equal [3, 4, 6], school.to_hash.keys
  end
end

si en lugar de

self.school = {}

usas

self.school = Hash.new([])

te ahorras de hacer el ternario en la linea 16