```ruby
# frozen_string_literal: true

# rectangle on the surface of the earth, with borders: north, south, east, west
# used mostly (exclusively?) by model scopes
class Box
  attr :north, :south, :east, :west

  def initialize(north: nil, south: nil, east: nil, west: nil)
    @north = north
    @south = south
    @east = east
    @west = west
  end

  def valid?
    args_in_bounds? &&
      south <= north &&
      ((west <= east) || straddles_180_deg?)
  end

  def straddles_180_deg?
    west > east && (west >= 0 && east <= 0)
  end

  # Return a new box with edges expanded by delta
  # Useful for dealing with float rounding errors when
  # making comparisons to edges
  def expand(delta)
    Box.new(north: north + delta,
            south: south - delta,
            east: east + delta,
            west: west - delta)
  end

  ##############################################################################

  private

  def args_in_bounds?
    south&.between?(-90, 90) && north&.between?(-90, 90) &&
      west&.between?(-180, 180) && east&.between?(-180, 180)
  end
end
```

Revise BoxTest to get tests passing
user
```ruby
# frozen_string_literal: true

# rectangle on the surface of the earth, with borders: north, south, east, west
# used mostly (exclusively?) by model scopes
class Box
  attr :north, :south, :east, :west

  def initialize(north: nil, south: nil, east: nil, west: nil)
    @north = north
    @south = south
    @east = east
    @west = west
  end

  def valid?
    args_in_bounds? && south <= north
  end

  def straddles_180_deg?
    west > east
  end

  # Return a new box with edges expanded by delta
  # Useful for dealing with float rounding errors when
  # making comparisons to edges
  def expand(delta)
    Box.new(north: north + delta,
            south: south - delta,
            east: east + delta,
            west: west - delta)
  end

  ##############################################################################

  private

  def args_in_bounds?
    south&.between?(-90, 90) && north&.between?(-90, 90) &&
      west&.between?(-180, 180) && east&.between?(-180, 180)
  end
end
```
assistant