wait_steps.rb

require "timeout"

module WaitSteps
  extend RSpec::Matchers::DSL

  matcher :become_true do
    match do |block|
      begin
        Timeout.timeout(Capybara.default_wait_time) do
          sleep(0.1) until value = block.call
          value
        end
      rescue TimeoutError
        false
      end
    end
  end
end

This become_truthy helped me here. I customized a bit and it's just perfect. Thanks.

# spec_helper.rb
RSpec::Matchers.define :wait_until do |event_name|
  supports_block_expectations

  match do |block|
    begin
      Timeout.timeout(Capybara.default_max_wait_time) do
        sleep(0.05) until value = block.call
        value
      end
    rescue TimeoutError
      false
    end
  end
end

# features/location_ajax_autocomplete_spec.rb
require 'rails_helper'

feature 'Products GET #location', type: :feature do
  context 'with valid params' do
    scenario 'populates location after requesting in the api' do
      visit location_path

      fill_in 'location', with: 'Munich'

      wait_until { expect(page.body).to have_selector('li', class: 'location-item', count: 10) }
    end
  end
end