Testing with Fixtures

Learning Goals

• Implement a test helper
• Understand what test fixtures are and why they are useful
• Implement a test fixture

Slides here

Vocabulary

• Test Fixture

Warmup

• What makes testing easy?
• What makes testing hard?
• What challenges are you finding in testing Black Thursday?
• What might be some disadvantages to testing with a large dataset?
• What might be some alternatives?

Fixtures

You may not have fully noticed yet, but all that data processing we’re testing is really starting to affect our test suite’s performance. Let’s see if we can fix that up.

Basics

• Create smaller copies of files you’ll use in production
• Mimic a request to an external dependency within testing environment, making calls

Let’s set up a quick learning_fixtures project folder in our classwork directory complete with lib, data, and test directories.

We’re going to test-drive iterating over an absurdly long CSV.

But first, you’ll need to download this and save it in data.

Let’s use our CSV knowledge to create a hash based on the values contained in the CSV. We’ll just create a new hash based on a few key headers and redefine those values with each new row in our CSV. We’ll assert that the last "EPISODE" key’s value is from the last row of the CSV.

Seem pointless? We really just want to create a task that will take significantly long to perform, but would be relatively quick with a customized fixture.

# test/bob_test.rb

require 'minitest'
require 'minitest/autorun'
require 'minitest/pride'
require './lib/bob'

class BobTest < Minitest::Test
  def test_it_exists
    assert_instance_of Bob, Bob.new('./data/bob_elements.csv')
  end

  def test_time_to_run_long_iteration
    bob = Bob.new('./data/bob_elements.csv')

    assert_equal "S31E13", bob.final_episode
  end
end

Test Helpers

Tired of writing all those require statements at the top of each file? Let’s start thinking of our test files in a more DRY fashion.

Creating a test_helper.rb that our test files require allows us to store the rest of our repetitive setup in one centralized location.

# test/test_helper.rb

require 'minitest'
require 'minitest/autorun'
require 'minitest/pride'

Now you can remove that from your test and simply

require './test/test_helper'

# lib/bob.rb

require 'csv'
require 'pry'

class Bob
  
  def initialize(filepath)
    @filepath = filepath
  end

  def final_episode
    current_episode = {}
    
    CSV.foreach(@filepath, headers: true, header_converters: :symbol) do |row|
      current_episode['episode_number'] = row[:episode]
    end
    
    current_episode['episode_number']
  end
  
end

> Want to see approximately how long your tests take to run? Use the `-v` flag when running your tests and Minitest will be more verbose.

Once this is running, let’s speed things up with a bob_elements_truncated.csv fixture.

.
├── data
|   └── bob_elements.csv
├── lib
|   └── bob.rb
└── test
    ├── bob_test.rb
    ├── test_helper.rb
    └── fixtures
        └── bob_elements_truncated.csv

Wrap-up

• Why would you want to use a test helper?
• How can test fixtures improve your testing suite?
• How many lines of data should you include in your fixture files?