Using test-driven development with RSpec, we'll create the following classes:
- Has a length and a width
- Has methods that return its perimeter and area
- Has a radius
- Has methods that return its circumference and area
- Has three side lengths
- Has methods that return its perimeter and area
- Has a method that determines whether the triangle is valid (hint: use the Inequality Theorem)
Bonus: Prevent invalid triangles from being created in the first place by raising an ArgumentError. Be sure to do this in a test-driven way by changing your tests first to describe the new behavior before changing any code. The method that checks for validity can now be private – why is this?
Bonus: Implement similar validity checks for Rectangles and Circles using a private method.