migration

class CreateOpeningHours < ActiveRecord::Migration
  def change
    create_table :opening_hours do |t|
      t.timestamps

      t.integer :week_day, null: false
      t.datetime :start_time, null: false
      t.datetime :end_time, null: false
    end

    add_index :opening_hours, :week_day
  end
end

opening_hour_test.rb

require 'test_helper'

describe OpeningHour do
  parallelize_me!

  it 'requires all attributes to be set' do
    invalid_opening_hour = OpeningHour.new
    assert !invalid_opening_hour.valid?
  end

  describe '#active?' do
    it 'returns true when current time is between opening and closing time' do
      active_opening_hour = OpeningHour.new week_day: Time.now.wday, start_time: Time.now - 5.hours, end_time: Time.now + 2.hours
      assert active_opening_hour.active?
    end

    it 'returns true when current time is between opening and closing time even if after midnight' do
      active_opening_hour = OpeningHour.new week_day: Time.now.wday, start_time: Time.now - 2.hours, end_time: Time.now.end_of_day + 2.hours
      Time.stub :now, Time.now.end_of_day + 1.hour do
        assert active_opening_hour.active?
      end
    end

    it 'returns false when current time is before opening time' do
      inactive_opening_hour = OpeningHour.new week_day: Time.now.wday, start_time: Time.now + 2.hours, end_time: Time.now.end_of_day + 5.hours
      assert !inactive_opening_hour.active?
      # not sure if this works..
      # assert_false inactive_opening_hour.active?
    end

    it 'returns false when current time is after closing time' do
      inactive_opening_hour = OpeningHour.new week_day: Time.now.wday, start_time: Time.now - 5.hours, end_time: Time.now.end_of_day - 2.hours
      assert !inactive_opening_hour.active?
      # not sure if this works..
      # assert_false inactive_opening_hour.active?
    end
  end
end

OpeningHour.rb

class OpeningHour < ActiveRecord::Base
  validates_presence_of :week_day, :start_time, :end_time

  scope :today, -> {where(week_day: Time.now.wday)}

  def active?
    week_day == Time.now.wday && Time.now === start_time..end_time
  end
end

output

# Running tests:

EEEE.

Finished tests in 0.061518s, 81.2770 tests/s, 16.2554 assertions/s.

  1) Error:
OpeningHour::#active?#test_0004_returns false when current time is after closing time:
ArgumentError: bad value for range
    app/models/opening_hour.rb:7:in `active?'
    test/models/opening_hour.rb:33:in `block (3 levels) in <top (required)>'

  2) Error:
OpeningHour::#active?#test_0002_returns true when current time is between opening and closing time even if after midnight:
NoMethodError: undefined method `stub' for Time:Class
    test/models/opening_hour.rb:19:in `block (3 levels) in <top (required)>'

  3) Error:
OpeningHour::#active?#test_0001_returns true when current time is between opening and closing time:
ArgumentError: bad value for range
    app/models/opening_hour.rb:7:in `active?'
    test/models/opening_hour.rb:14:in `block (3 levels) in <top (required)>'

  4) Error:
OpeningHour::#active?#test_0003_returns false when current time is before opening time:
ArgumentError: bad value for range
    app/models/opening_hour.rb:7:in `active?'
    test/models/opening_hour.rb:26:in `block (3 levels) in <top (required)>'

5 tests, 1 assertions, 0 failures, 4 errors, 0 skips