Object Oriented Basics (Ruby)

Define a class BookInStock which represents a book with an ISBN number, isbn, and price of the book as a floating-point number, price, as attributes. The constructor should accept the ISBN number (a string, since in real life ISBN numbers can begin with zero and can include hyphens) as the first argument and the price as the second argument, and should raise ArgumentError (one of Ruby's built-in exception types) if the ISBN number is the empty string or if the price is less than or equal to zero. Include the proper getters and setters for these attributes. Include a method price_as_string that returns the price of the book formatted with a leading dollar sign and two decimal places, that is, a price of 20 should format as $20.00 and a price of 33.8 should format as $33.80. Check out formatted string methods in Ruby.