Jscov

Collect JavaScript code coverages. It works with istanbul.

Installation

Add this line to your application's Gemfile:

gem 'jscov'

And then execute:

$ bundle

Or install it yourself as:

$ gem install jscov

Usage

Install babel-plugin-istanbul.

$ yarn add -D babel-plugin-istanbul

And setup it. In babel.config.js:

module.exports = function (api) {
  // ....
  return {
    plugins: [
      // ...
      isTestEnv && 'babel-plugin-istanbul' // Add this
    ].filter(Boolean)
  }
}

Add Jscov middleware to rails middleware stack. Add the following in config/environments/test.rb:

[MyRailsApp]::Application.configure do |config|
  ...
  config.middleware.use Jscov::RackMiddleware
  ...
end

Load rspec helper. In spec/rails_helper.rb:

require 'jscov/rspec'

Configure selenium to capture the output of console.log:

RSpec.configure do |config|
  config.before(type: :system) do
    caps = Selenium::WebDriver::Remote::Capabilities.chrome(
      'goog:loggingPrefs' => { browser: 'ALL' }
    )
    driven_by :selenium, using: :headless_chrome, options: { capabilities: caps }
  end
end

And configure rspec to save coverage files after each examples:

RSpec.configure do |config|
  config.after(type: :system) do
    Jscov.save!
  end
end

Run NODE_ENV=test RAILS_ENV=test bin/rails assets:precompile for generating js codes that applied istanbul:

NODE_ENV=test RAILS_ENV=test bin/rails assets:precompile

OK, run rspec! It will dump collected coverage files in tmp/jscov. The collected coverages can be output as a report using nyc.

$ npx nyc report --temp-dir=tmp/jscov

Tips

Selenium's logs.get(:browser) is a destructive method. jscov depends on it. If you use it out of jscov, it will affect to result of jscov, and vice versa.

You can pass browser logs to Jscov.save! to avoid this issue:

logs = Capybara.current_session.driver.browser.logs.get(:browser)
Jscov.save!(logs: logs)

If you use multiple capybara sessions, you can pass your capybara sessions to Jscov.save! to save coverages that collected on your sessions:

Jscov.save!(session: your_capybara_session)

Vue.js

To collect coverage for .vue files, you will need to change the configurations.

In babel.config.js:

module.exports = function (api) {
  // ....
  return {
    plugins: [
      // ...
      // Add below
      isTestEnv && [
        'babel-plugin-istanbul',
        {
          extension: ['.js', '.vue']
        }
      ]
    ].filter(Boolean)
  }
}

And, you need to add an argument to nyc:

$ npx nyc report --temp-dir=tmp/jscov --extension=.vue

Configuration

You can configure the following values.

Jscov.configure do |config|
  # config.coverage_report_dir_path = Rails.root.join("tmp/jscov")
end

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/kzkn/jscov.

License

The gem is available as open source under the terms of the MIT License.