Don’t set = 'Pacific Time (US & Canada)'. It will change the Time Zone for the rest of your tests.

Instead, you can implement a RSpec callback on that sets the timezone only for the specific test.

# spec/support/timezone.rb

config.around :example, :tz do |example|
  Time.use_zone(example.metadata[:tz]) { }

Then you can simply set the tz metadata with the timezone you want to use on your test.

it 'displays start time with user timezone', tz: 'Pacific Time (US & Canada)' do
  user_timezone = 'Brasilia'
  start_date ='2017-12-31 23:00:00')
  event = 'World Cup', start_date_time: start_date)
  name_with_start_date = event.name_with_start_date(user_timezone)

  expect(name_with_start_date).to eq 'World Cup (Jan 1, 2018)'


RSpec Documentation - metadata

Using RSpec metadata (rossta)