exercism/ruby/hello-world/GETTING_STARTED.md

Getting Started

These exercises lean on Test-Driven Development (TDD), but they're not an exact match. If you want a gentle introduction to TDD using minitest in Ruby, see the "Intro to TDD" over at JumpstartLab: http://tutorials.jumpstartlab.com/topics/testing/intro-to-tdd.html

The following steps assume that you are in the same directory as the test suite.

You must have the minitest gem installed:

$ gem install minitest

Step 1

Run the test suite. It's written using the Minitest framework, and can be run with ruby:

$ ruby hello_world_test.rb

This will fail, complaining that there is no file called hello_world.

To fix the error create an empty file called hello_world.rb in the same directory as the hello_world_test.rb file.

Step 2

Run the test again. It will give you a new error, since now the file exists, but is empty and does not contain the expected code.

Depending on what platform you are on, the error will look different, but the way to fix it will be the same.

On Windows, it will complain about:

syntax error, unexpected end-of-input, expecting '('

On OS X and Linux, the error will be something like:

# Running:

E

Finished in 0.001328s, 753.0121 runs/s, 0.0000 assertions/s.

  1) Error:
HelloWorldTest#test_say_hi:
NameError: uninitialized constant HelloWorldTest::HelloWorld
Did you mean?  HelloWorldTest
    hello_world_test.rb:19:in `test_say_hi'

1 runs, 0 assertions, 0 failures, 1 errors, 0 skips

Within the first test, we are referencing a constant named HelloWorld when we say HelloWorld.hello. When Ruby sees a capitalized name like HelloWorld, it looks it up in a big huge list of all the constants it knows about, to see what it points to. It could point to anything, and often in Ruby we have constants that point to definitions of classes or modules.

When it looks HelloWorld up in its list, it doesn't find anything, so we need to make one.

Fixing the Error

To fix it, open up the hello_world.rb file and add the following code:

class HelloWorld
end

Step 3

Run the test again.

1) Error:
HelloWorldTest#test_no_name:
NoMethodError: undefined method `hello' for HelloWorld:Class
    hello_world_test.rb:20:in `test_no_name'

This time we have a HelloWorld, but we're trying tell it to hello, and HelloWorld doesn't understand that message.

Open up hello_world.rb and add a method definition inside the class:

class HelloWorld
  def self.hello
  end
end

Step 4

Run the test again.

1) Failure:
HelloWorldTest#test_no_name [hello_world_test.rb:11]:
When given no name, we should greet the world.
Expected: "Hello, World!"
  Actual: nil

Up until now we've been getting errors, this time we get a failure.

An error means that Ruby cannot even run properly because of things like missing files or syntax errors, or referring to things that don't exist.

A failure is different. A failure is when Ruby is running just fine and the test is expecting one outcome, but getting another.

The test is expecting the hello method to return the string "Hello, World!". The easiest way to make it pass, is to simply stick the string "Hello, World!" inside the method definition.

Step 5

Run the test again.

If it fails you're going to need to read the error message carefully to figure out what went wrong, and then try again.

If it passes, then you're ready to move to the next step.

Submit

When everything is passing, you can submit your code with the following command:

$ exercism submit hello_world.rb