Hello World

Hello World #

You can find all the code for this chapter here

It is traditional for your first program in a new language to be Hello, World.

  • Create a folder wherever you like
  • Put a new file in it called hello.rb and put the following code inside it
def main
    print("Hello, world")


To run it type ruby hello.rb.

How it works #

When you write a program in Ruby just can define a method and after that just call it.

The def keyword is how you define a function with a name and a body.

Ruby provide out of the box a function called print that we use to print out to the console.

How to test #

How do you test this? It is good to separate your “domain” code from the outside world (side-effects).

The print is a side effect (printing to stdout) and the string we send in is our domain.

So let’s separate these concerns so it’s easier to test

def hello
  return "Hello, world"

def main


We have created a new function again with def called hello.

Now create a new file called hello_test.rb where we are going to write a test for our hello function

require "minitest/autorun"

require_relative "hello"

class TestHello < Minitest::Test
  def test_hello
    assert_equal hello, "Hello, world"