Mock browser time in feature tests

Rails
1

Sometimes it could be necessary to mock your browser time for your tests if your app relies on JS (e.g. if using React).

An example scenario:

scenario "mocking browser time...", :js, :mock_browser_time do
  travel_to Date.new(2017, 6, 1) do
    visit root_path
    ...
  end
end

First, we’ll need to add a couple of helper methods for Capybara:

Capybara.class_eval do
  def self.mock_browser_time(&block)
    @mock_browser_time = true
    yield block
    @mock_browser_time = false
  end

  def self.mock_browser_time?
    @mock_browser_time
  end
end

And then in an around hook for RSpec:

RSpec.configure do |config|
  config.around(:each, :mock_browser_time) do |example|
    Capybara.mock_browser_time { example.run }
  end
end

This will allow us to mock the browser time in our tests if needed using the tag mock_browser_time. The last bit is the code needed for actually mocking the time in the browser. Previous work could be find here

- if Rails.env.test? && defined?(Capybara) && Capybara.mock_browser_time?
  - unix_millis = (Time.now.to_f * 1000.0).to_i

  :javascript
    lolex.install({ now: #{unix_millis}, shouldAdvanceTime: true });

The shouldAdvanceTime option was needed for us, it will depend on your codebase.

Also if your time works in different timezones be sure to add a common timezone for your tests. Add this to your rails_helper file:

ENV["TZ"] = "UTC"

References:

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