character.rb

character.rb

class Character < ApplicationRecord
  TEAMS_FOR_UNITS = {
    knight: 1,
    mage: 1,
    medusa: 2,
    jinn: 2
  }
  
  validates :team, presence: true
  validates :unit, presence: true
  validates :unit, acceptance: { accept: ['mage', 'knight', 'medusa', 'jinn']}
  validate :correct_team
  
  before_validation :set_team

  private
  def correct_team
    errors.add(:unit, "Unit shoild match team") unless TEAMS_FOR_UNITS[unit.to_sym] == team
  end
  
  def set_team
    self.team = TEAMS_FOR_UNITS[unit.to_sym] if self.team.nil?
  end

end  

character_test.rb

class AdminUserTest < ActiveSupport::TestCase

  def test_team_auto_select
    character = Character.new(unit: 'knight')
    character.save
    assert_equal 1, character.team, 'Expected team to be auto selected'
  end
  
  def test_wrong_unit_rejected
    character = Character.new(unit: 'sknight')
    character.save
    refute character.valid?, 'Character should be invalidated for wrong unit'
  end

  def test_wrong_team_rejected
    character = Character.new(unit: 'knight', team: -1)
    character.save
    refute character.valid?, 'Character should be invalidated for wrong team'
  end

  def test_wrong_team_and_unit_match
    character = Character.new(unit: 'knight', team: 2)
    character.save
    refute character.valid?, 'Character should be invalidated for wrong team-unit pair'
  end

  def test_correct_team_and_unit_match
    character = Character.new(unit: 'medusa', team: 2)
    character.save
    assert character.valid?, 'Character should be saved with explicit unit-team pair'
    assert_equal 2, character.team, 'Explicitly defined team should be present'
  end
  
end