Introduction to RSpec and Test-Driven Development using Factorial

factorial.rb

# Given an integer greater than or equal to zero
def factorial(n)
  return 1 if n <= 1

  product = 1
  index = n

  while index > 1
    product *= index
    index -= 1
  end

  product
end

factorial_spec.rb

require_relative '../factorial'

describe "Factorial" do
  it "computes the factorial of 0" do
    expect(factorial(0)).to eq 1
  end
  it "computes the factorial of 1" do
    expect(factorial(1)).to eq 1
  end
  it "computes the factorial of 2" do
    expect(factorial(2)).to eq 2
  end
  it "computes the factorial of 3" do
    expect(factorial(3)).to eq 6
  end
  it "computes the factorial of 4" do
    expect(factorial(4)).to eq 24
  end
  it "computes the factorial of 5" do
    expect(factorial(5)).to eq 120
  end
  it "computes the factorial of 6" do
    expect(factorial(6)).to eq 720
  end
  it "computes the factorial of 7" do
    expect(factorial(7)).to eq 5040
  end
end

I like writing factorial as recursive:

def factorial(n): if n in [0,1]: return 1 else: return n * factorial(n -1)