```ruby
require 'spec_helper'

describe BusStop do
  describe 'assign_completion_timestamp' do
    context 'bus stop is completed' do
      # need some time cop up in here
      it 'assigns the current time to completed_at' do
      end
    end
    context 'bus stop is not completed' do
      it 'assigns nil to completed at' do
      end
    end
  end

  describe 'decide_if_completed_by' do
    context 'bus stop completed attribute changed' do
      context 'bus stop is completed' do
        it 'assigns user to completed by' do
          stop_1 = create :bus_stop, completed: true
          stop_1.update! completed: false
          # how to access current user
          # stop_1.decide_if_completed_by current_user
          # user.fetch(:completed_by).to be current_user
        end
      end
      context 'bus stop is not completed' do
        it 'assigns nil to completed by' do
        end
      end
    end
  end
end
```

Make sure to test these models
user
```ruby
require 'spec_helper'

describe BusStop do
  describe 'assign_completion_timestamp' do
    context 'bus stop is completed' do
      # need some time cop up in here
      it 'assigns the current time to completed_at' do
      end
    end
    context 'bus stop is not completed' do
      it 'assigns nil to completed at' do
      end
    end
  end

  describe 'decide_if_completed_by' do
    context 'bus stop completed attribute changed' do
      context 'bus stop is completed' do
        it 'assigns user to completed by' do
          stop_1 = create :bus_stop, completed: true
          stop_1.update! completed: false
          # how to access current user
          # stop_1.decide_if_completed_by current_user
          # user.fetch(:completed_by).to be current_user
        end
      end
      context 'bus stop is not completed' do
        it 'assigns nil to completed by' do
        end
      end
    end
  end

  describe 'completed scope' do
  end

  describe 'not_started scope' do
  end

  describe 'pending scope' do
  end
end
```
assistant