Why Write Rails View Tests

Published | Last updated | About 6 minutes to read

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There are many ways to test a Ruby on Rails application, but there is one way that is not so often discussed. That is the way of testing Rails views. Yes - there are controller, model, and other types of tests, but we rarely see the view layer tests. Let’s give them more attention and see what they are all about.

You might ask - well, why don’t you write integration tests and test view layer with them? I could, but running integration tests can be slow, and writing a simple view ‘unit’ test can be more straightforward. Plus, RSpec has great support for writing a view spec. What is even more interesting, I created an example project to test these out. Let’s see what I found out.

New Project, Who This

I created new Rails 6.1 project, installed RSpec, and generated the Book model with:

bin/rails generate scaffold Book title:string description:text download_url:string status:string

And look at what I got generated:

...

    create      spec/views/books/edit.html.erb_spec.rb
    create      spec/views/books/index.html.erb_spec.rb
    create      spec/views/books/new.html.erb_spec.rb
    create      spec/views/books/show.html.erb_spec.rb

...

If we take a look at one of the specs, we can find the following code:

# spec/views/books/index.html.erb_spec.rb

require 'rails_helper'

RSpec.describe "books/index", type: :view do
  before(:each) do
    assign(:books, [
      Book.create!(
        title: "Title",
        description: "MyText",
        download_url: "Download Url",
        status: "Status"
      ),
      Book.create!(
        title: "Title",
        description: "MyText",
        download_url: "Download Url",
        status: "Status"
      )
    ])
  end

  it "renders a list of books" do
    render
    assert_select "tr>td", text: "Title".to_s, count: 2
    assert_select "tr>td", text: "MyText".to_s, count: 2
    assert_select "tr>td", text: "Download Url".to_s, count: 2
    assert_select "tr>td", text: "Status".to_s, count: 2
  end
end

There’s the type: view that indicates the special type of specs. We will go into this later a bit. You can distinguish assign and render methods that indicate that they are defined internally and not something we should provide. But, there is also one thing sticking into my eyes as I go through this test.

What’s interesting here, this assert_select matcher looks a bit “deprecated” or like it is not from the RSpec world. There’s no class expect(...).to formation. What happened here is that the template for generating these specs got a bit dusty. It didn’t change from 2010, when it was originally pushed to the repo. You can find the commit that brought the assert_select here on GitHub.

No worries, I didn’t see many projects using view specs, let alone generating models and relying on those generated view specs. I guess that is why nobody took out the time to refactor or improve the existing template. But, since this blog post is about focusing our attention on Rails view testing, let us try to do just that.

Spring Cleaning

If we take a look at the docs for view specs in RSpec, we can see that almost all of them use the following:

expect(rendered).to match /something/

We can use match and include from RSpec. What we get is a test that looks like this:

# spec/views/books/index.html.erb_spec.rb

require 'rails_helper'

RSpec.describe "books/index", type: :view do
  before(:each) do
    assign(:books, [
      Book.create!(
        title: "Rails Testing",
        description: "How to test Ruby on Rails applications.",
        download_url: nil,
        status: "draft"
      ),
      Book.create!(
        title: "Rails Patterns",
        description: "A book about patterns and anti-patterns in Ruby on Rails.",
        download_url: "rails-patterns.com/download",
        status: "published"
      )
    ])
  end

  it "renders a list of books" do
    render

    expect(rendered).to match(/Rails Testing/)
    expect(rendered).to include("Rails Patterns")

    expect(rendered).to match(/How to test Ruby on Rails applications./)
    expect(rendered).to include("A book about patterns and anti-patterns in Ruby on Rails.")

    expect(rendered).to include("rails-patterns.com/download")

    expect(rendered).to include("published")
  end
end

The previous test feels more like a RSpec spec. But, we can notice is that we lost that ability to check whether the actual content is inside a certain HTML tag. assert_select gives us more flexibility in matching the expected result. There’s more options you can pass to assert_select in its docs. I suggest you choose the option you feel gives you more control.

Utilizing Capybara

If you have Capybara installed, you can utilize its selectors like so:

require "rails_helper"

RSpec.describe "books/index", type: :view do
  before(:each) do
    assign(:books, [
      Book.create!(
        title: "Rails Testing",
        description: "How to test Ruby on Rails applications.",
        download_url: nil,
        status: "draft"
      ),
      Book.create!(
        title: "Rails Patterns",
        description: "A book about patterns and anti-patterns in Ruby on Rails.",
        download_url: "rails-patterns.com/download",
        status: "published"
      )
    ])
  end

  it "renders a list of books" do
    render

    expect(rendered).to have_selector("tr>td", text: "Rails Testing")
    expect(rendered).to have_selector("tr>td", text: "Rails Patterns")

    expect(rendered).to have_selector("tr>td", text: "How to test Ruby on Rails applications")
    expect(rendered).to have_selector("tr>td", text: "A book about patterns and anti-patterns in Ruby on Rails.")

    expect(rendered).to have_selector("tr>td", text: "rails-patterns.com/download")

    expect(rendered).to have_selector("tr>td", text: "published")
  end
end

Now, you get both RSpec expect(...).to, and you get the granularity of asserting that text is inside a table row. You can find all of the code and examples in the repo here. But why would you use any of these? Let’s discuss below.

Why View Specs

We skimmed over a couple of reasons why you would write a view spec. The idea is to test some conditional logic you have in your views or partials. Writing an integration test that covers all the branches inside your views can be slow to run and painful to write. The view specs bring a great balance between:

  • 💸 cost of development,
  • 🏍 speed of execution, and
  • 🔀 conditional rendering coverage.

Of course, you might not need view specs at all if you have decorators and view models, form objects, and all other goodies that can move the logic out of the view for you. But, sometimes, in the real world, not every code base is perfectly designed, and you have to cut corners from time to time.

Whether it is some kind of stakeholder breathing down your neck. Or it’s the complicated legacy partial that can’t be so easily extracted to a design of your choice. Whatever the reason is, you might opt-in for the view spec to move fast and have the logic tested.

And when that day comes (or it already came), you can resort back to this blog post and use it to your liking.

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Catch you in the next one, cheers.


Tagged as: RailsTesting

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