Why DSLs are a necessary part of learning Rails testing

by Jason Swett,

If you want to be a competent Rails tester, there are a lot of different things you have to learn. The things you have to learn might be divided into three categories.

The first of these three categories is tools. For example, you have to choose a testing framework and learn how to use it. Then there are principles, such as the principle of testing behavior vs. implementation. Lastly, there are practices, like the practice of programming in feedback loops.

This post will focus on the first category, tools.

For better or worse, the testing tools most commercial Rails projects use are RSpec, Factory Bot and Capybara. When developers who are new to testing (and possibly Ruby) first see RSpec syntax, for example, they’re often confused.

Below is an example of a test written using RSpec, Factory Bot and Capybara. To a beginner the syntax may look very mysterious.

describe "Signing in", type: :system do
  it "signs the user in" do
    user = create(:user)
    visit new_user_session_path
    fill_in "Username", with: user.username
    fill_in "Password", with: user.password
    click_on "Submit"
    expect(page).to have_content("Sign out")
  end
end

The way to take the above snippet from something mysterious to something perfectly clear is to learn all the details of how RSpec, Factory Bot and Capybara work. And doing that will require us to become familiar with domain-specific languages (DSLs).

For each of RSpec, Factory Bot and Capybara, there’s a lot to learn. And independently of those tools, there’s a lot to be learned about DSLs as well. Therefore I recommend learning a bit about DSLs separately from learning about the details of each of those tools.

Here are some posts that can help you learn about DSLs. If you’re learning testing, I suggest going through these posts and seeing if you can connect them to the code you see in your Rails projects’ codebases. As you gain familiarity with DSL concepts and the ins and outs of your particular tools, your test syntax should look increasingly clear to you.

Understanding Ruby Proc objects
Understanding Ruby closures
Understanding Ruby blocks
What the ampersand in front of &block means
The two common ways to call a Ruby block
How map(&:some_method) works
How Ruby’s instance_exec works
How Ruby’s method_missing works

Learning how Ruby DSLs work can be difficult and time-consuming but it’s well worth it. And if you’re using testing tools that make use of DSLs, learning about DSLs is a necessary step toward becoming a fully competent Rails tester.

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