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:

ESSS

Finished in 0.001539s, 2599.0903 runs/s, 0.0000 assertions/s.

1) Error:
HelloWorldTest#test_no_name:
NameError: uninitialized constant HelloWorldTest::HelloWorld
  hello-world/hello_world_test.rb:5:in `test_no_name'

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

Understanding Test Failures

Whether you are on Windows, Mac OS X or Linux, you will eventually be faced with errors and failures that look a lot like the Mac OS X / Linux error above.

The letters ESSS show that there are four tests altogether, that one of them has an error (E), and that three of them are skipped (S).

The goal is to have four passing tests, which will show as four dots: .....

The tests are run in randomized order, which will cause the letters to display in random order as well.

Step 3

Run the test again.

1) Error:
HelloWorldTest#test_no_name:
NoMethodError: undefined method `hello' for HelloWorld:Class
    hello_world_test.rb:5: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 6

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.

Open the hello_world_test.rb file, and find the word "skip". All but the first test start with "skip", which tells Minitest to ignore the test. This is so that you don't have to deal with all the failures at once.

To activate the next test, delete the "skip", and run the test suite again.

Wash, Rinse, Repeat

Delete one "skip" at a time, and make each test pass before you move to the next one.

Submit

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

$ exercism submit hello_world.rb