Julia Evans

Day 23: a little Rails testing

I’ve been working on a little Rails app to manage a bunch of virtual machines that run programming puzzles, and in the last couple days I ran into a problem I run into a lot: I forgot about testing!

here’s how it goes:

  1. start writing some code with no tests, think “this is fine”
  2. 2 days later, realize I’m spending a lot of time manually testing and fixing the same bug 3 times because I broke it again
  3. remember that automated testing exists
  4. write tests and everything is 10x better

A few small nice things that I’ve found in my first day or two of doing testing in Rails:

my Rails app comes with tests!

I’ve haven’t really used Rails much before, and when I started writing tests I noticed that rails generate scaffold Puzzle had generated a bunch of tests for me for the Puzzle controller!

This was really nice because it gave me a template to start from

there are fixtures!

Every model has a corresponding file called test/fixtures/MODEL_NAME.yml that has a bunch of data used to create test objects. For example, here are some fixtures for my VirtualMachineInstance model:

   email: manuela@example.com
   email: rishi@example.com

This means that I can quickly create a test object like this:

@user = users(:rishi)

there are authentication helpers to help manage logins!

I’m using a gem called Devise right now to handle logins, and it comes with a bunch of test helpers to pretend that I’m logged in to the site when accessing a page. This is super useful in integration tests!

Here’s what that looks like

  setup do
    @user = users(:rishi)
    login_as(@user, :scope => :user)

mocking HTTP requests is easy

I have some code in my project that talks to an API to launch virtual machine instances. I obviously don’t actually want to launch VM instances in my tests (could get expensive!), so I wanted to mock out the calls to the API. Here’s how that works:

stub_request(:get, "https://api.digitalocean.com/v2/account/keys?page=1&per_page=20").
  to_return(status: 200, body: '{"ssh_keys":[],"links":{},"meta":{"total":2}}')

The nice thing is that WebMock.disable_net_connect! prevents Ruby from making any external API requests, and if one happens then it prints out an example of some code I could write to mock that request.

integration tests seem easy at first

I was spending a lot of time clicking on links and making sure that if it worked if I went to X page and then Y page from there.

I was surprised by how easy Rails makes it to write integration tests! Here’s an example of an integration test that I have that makes sure that right after you start a puzzle (which launches an instance), the instance’s status is “pending”. So little code!

test "status is pending right after instance started" do
    get '/puzzles/1/start'
    get '/instances/220816290/status'
    assert_response :success
    assert_equal({"status" => "pending"}, response.parsed_body)

This code definitely has a “magical Ruby” feel but I don’t really mind and it’s fun to write so far.

that’s all!

One thing I really appreciate about Rails is that there are like 15 million blog posts and Stack Overflow answers about using it, which has made it pretty easy so far to get all my questions answered.

It really feels like if I’m confused about something, many thousands of people have been confused about the exact same thing and have written about it in 1000 different places, which is a nice change of pace from some of the weirder things I’ve tried to learn about.

Day 22: getting OAuth to work in Rails Day 24: a short talk about blogging myths, and a debugging tip