Uninitialized constant error in Ruby class - ruby-on-rails

Question

I have these two classes in RubyMine:
book.rb:
class Book
def initialize(name,author)
end
end
test.rb:
require 'book'
class teste
harry_potter = Book.new("Harry Potter", "JK")
end
When I run test.rb, I get this error:
C:/Users/DESKTOP/RubymineProjects/learning/test.rb:3:in `<class:Test>': uninitialized constant Test::Book (NameError)
from C:/Users/DESKTOP/RubymineProjects/learning/test.rb:1:in `<top (required)>'
from -e:1:in `load'
from -e:1:in `<main>'

Answer 1

You're getting the error because your require 'book' line is requiring some other book.rb from somewhere else, which doesn't define a Book class.
Ruby does not automatically include the current directory in the list of directories it will search for a require so you should explicitly prepend a ./ if you want to require a file in the current directory, ie.
require './book'

Answer 2

You have defined the initialize method but forgot to assign the values into instance variables and a typo in your code triggered the error, fixed it as:
book.rb
class Book
def initialize(name,author)
#name = name
#author = author
end
end
test.rb
require './book'
class Test
harry_potter = Book.new("Harry Potter", "JK")
end
So, which book or resource are you following? I think you should at least complete a book to get proper knowledge of Ruby and Object Oriented Programming. I would suggest you 'The Book of Ruby' to start with.

Answer 3

In a Rails app this error can also be caused by renaming the class without renaming the file to match, which was my issue when I found this error:
book.rb
class Book
def initialize(name, author)
end
end
book_test.rb
class BookTest
harry_potter = Book.new("Harry Potter", "JK")
end