input: Write a function to develop a Python class called Rectangle that can represent a two-dimensional rectangle with a length and width. The class should include an initializer to set the length and width, and a method to calculate the area of the rectangle. Provide assert test cases to verify the functionality.
  assert Rectangle(4, 5).area()==20
  assert Rectangle(3, 3).area()==9
  assert Rectangle(0, 5).area()==0
  assert Rectangle(1, 1).area()==1
  assert Rectangle(2, 6).area()==12
output: class Rectangle:
      def __init__(self, length, width):
          self.length = length
          self.width = width
      
      def area(self):
          return self.length * self.width