Test ActiveRecord callbacks

team.rb

class Team < ActiveRecord::Base
  has_many :users

  validates :name, presence: true, uniqueness: true

  before_destroy :clear_team_members

  private

  # Clear team members when a team is destroyed
  def clear_team_members
    users = User.where(team: self)
    users.update_all(team_id: nil) if users.present?
    true
  end
end

team_spec.rb

# requires rspec >= 3.0
# requires factory_girl gem

describe '::destroy' do

  before :each do
    @team = create(:team)
    @team_member = create(:user, team_id: @team.id)
  end

  it 'should trigger clear_team_members on destroy' do
    expect(@team).to receive(:clear_team_members)
    @team.run_callbacks(:destroy)
  end

  it '#clear_team_members should set team members team_id to nil' do
    @team.run_callbacks(:destroy)
    @team_member.reload
    expect(@team_member.team_id).to be_nil
  end

end