input: Write a python function to fetch all books using graphene.
  assert fetch_books() == [book1, book2, book3]
  assert fetch_books() == [bookA, bookB]
  assert fetch_books() == []
output: def fetch_books():
      import graphene
  
      class Book(graphene.ObjectType):
          title = graphene.String()
          author = graphene.String()
  
      class Query(graphene.ObjectType):
          books = graphene.List(Book)
  
          def resolve_books(parent, info):
              # Mock data to simulate a database
              return [
                  Book(title="Book 1", author="Author 1"),
                  Book(title="Book 2", author="Author 2"),
                  Book(title="Book 3", author="Author 3"),
              ]
  
      schema = graphene.Schema(query=Query)
      query = '''
      query {
          books {
              title
              author
          }
      }
      '''
      result = schema.execute(query)
  
      # Extract the list of books from the result
      books_data = result.data['books']
      books = [Book(title=book['title'], author=book['author']) for book in books_data]
      return books