[Cucumber] how to use cucumber with a simple example

As my early post  [Cucumber] An brief introduction, Cucumber is an amazing testing tool and it is about Behaviour-Driven Development instead of Test-Driven Development. 

The book "The Cucumber Book" gives a very good explanation and useful of examles to illustrate the usages and functionalities in depths.

Based on that book's a good simple example, the following picture give the dictionary structure (left hand side ) and 3 of important files ( right hand side ) as follows:

"adding.feature" is file contained scenario ( test case )
"calc.rb" provides the calculation function for calculator_steps.rb
" calculator_steps.rb" provide the functions mapping to feature's script based on the key words: Given, When, and Then

Under the path, we run "cucumber" and then get the information as below:

Feature: Adding

  Scenario Outline: Add two numbers      # features/adding.feature:3
    Given the input "<input>"            # features/step_definitions/calculator_steps.rb:9
    When the calculator is run           # features/step_definitions/calculator_steps.rb:13
    Then the output should be "<output>" # features/step_definitions/calculator_steps.rb:18

    Examples:
      | input | output |
      | 2+2    | 4          |
      | 98+1  | 99        |

2 scenarios (2 passed)
6 steps (6 passed)
0m0.012s