For this quick tutorial lets assume you have an existing Rails app that already uses RSpec to which you have added a first Hyperstack component to try things out.

For your trial, you have created a very simple component that shows the number of orders shipped by your companies website:

class OrdersShipped < HyperComponent
  def format_number(number)
    number.to_s.reverse.gsub(/(\d{3})(?=\d)/, '\\1,').reverse

  render(DIV, class: 'orders-shipped') do
    format_number Order.shipped.count

Note that styling can be taken care of in the usual way by providing styles for the orders-shipped css class. All we care about here is the function of the component.

Meanwhile Order is an ActiveRecord Model that would look something like this:

class Order < ApplicationRecord
  scope :shipped, -> () { where(status: :shipped) }

Note that when using ActiveRecord models in your specs you will need to add the appropriate database setup and cleaner methods like you would for any specs used with ActiveRecord. We assume here that as each spec starts there are no records in the database

The OrdersShipped component can be mounted on any page of your site, and assuming the proper policy permissions are provided it will show the total orders shipped, and will dynamically increase in realtime.

A partial spec for this component might look like this:

require 'spec_helper'

describe 'OrdersShipped', :js do
  it 'dynamically displays the orders shipped' do
    mount 'OrdersShipped'
    expect(find('div.orders-shipped')).to have_content(0)
    Order.create(status: :shipped)
    expect(find('div.orders-shipped')).to have_content(1)
    expect(find('div.orders-shipped')).to have_content(0)

  it '#format method' do
    on_client { @comp = OrdersShipped.new }
    ['1,234,567', '123', '1,234'].each do |n|
      expect { @comp.format_number(n.gsub(',','').to_i) }
        .on_client_to eq(n)

If you are familiar with Capybara then the first spec should look similar to an integration spec. The difference is instead of visiting a page, we mount the OrdersShipped component on a blank page that hyper-spec will set up for us. This lets us unit test components outside of any application specific view logic.

Note that like Capybara we indicate that a client environment should be set up by adding the :js tag.

Once mounted we can use Capybara finders and matchers to check if our content is as expected. Because we are running on the server we can easily add and delete orders, and check the response on the UI.

The second spec shows how we can do some white box unit testing of our component. Instead of mounting the component we just create a new instance which will be invisible since it was not mounted. For this we use the on_client method.

The on_client method takes a block, and will compile that block using Opal, and execute it on the client. In this case we simply create a new OrderShipped instance, and assign it to an instance variable, which as you will see will continue to be available to us later in the spec.

Note, if you are an RSpec purist, you would probably prefer to see something like let be used here instead of an instance variable. Shall we say its on the todo list.

Now that we have our test component setup we can test its format_number method. To do this we put the test expression in a block followed by on_client_to. Again the block will be compiled using Opal, executed on the client, and the result will be returned to the expectation.

Notice that the server side variable n can be read (but not written) within the client block. All local variables, memoized variables, and instance variables can can be read in the client block as long as they represent objects that can be sensibly marshalled and unmarshalled.

This has covered the basics of Hyperspec - in summary:

  • The js tag indicates the spec will be using a client environment.

  • mount: Mount a component on a blank page. This replaces the visit method

    for unit testing components.

  • on_client: Execute Ruby code on the client (and return the result).

  • on_client_to: Execute the expectation block on the client, and then check

    the expectation (on the server.)

  • Instance variables retain their values between client execution blocks.

  • All variables accessible to the spec are copied to the client if possible.

There are many other features such as dealing with promises, passing data to and from a mounted component, using the Timecop gem, and working with a pry session. So read on.

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