scenario "Home page should display the current tenant's name" do
    Capybara.current_session.driver.reset!
    Capybara.default_host = 'tenant1'

    visit '/'
    page.should have_content("Welcome to Tenant1")

    Capybara.current_session.driver.reset!
    Capybara.default_host = 'tenant2'

    visit '/'
    page.should have_content("Welcome to Tenant 2")
  end

Although this post on testing subdomains with Capybara pointed me in the right direction, it may have been written for an older version of Capybara. The reason is that Capybara::Server.manual_host never was utilized.

Instead, I came up with this simpler(imo) solution: Just reset the current driver and assign a new default host.

You could even write a helper method that wraps those two lines to make it even cleaner!

This has only been tested with the rack-test driver and may not work with Culerity, Selenium, etc.