A example of a bad I18n rails test... Found some tests failing in a project because tests in different files would change I18n.locale, changes like this make your tests fail if not run in your standard order.

I18n_bad_test.rb

require File.dirname(__FILE__) + '/../test_helper'

class FakeTest < ActiveSupport::TestCase

  test "first de" do
    puts "about to be de: #{I18n.locale}"
    assert_equal 'en', "#{I18n.locale}"
    I18n.locale = 'de'
    assert true
  end

  test "then fr" do
    puts "about to be fr: #{I18n.locale}"
    assert_equal 'en', "#{I18n.locale}"
    I18n.locale = 'fr'
    assert true
  end

end

######
#
# A example of a bad I18n rails test... Found some tests failing in a project because tests in different
# files would change I18n.locale, changes like this make your tests fail if not run in your standard order.
# Don't modify I18n.locale in test with out a block the resets it or a teardown to set back to default.
#
######
# ruby test/unit/fake_test.rb
# 	Loaded suite test/unit/fake_test
# Started
# about to be de: en
# .about to be fr: de
# F
# Finished in 0.019414 seconds.

#   1) Failure:
# test_then_fr(FakeTest) [test/unit/fake_test.rb:14]:
# <"en"> expected but was
# <"de">.

# 2 tests, 3 assertions, 1 failures, 0 errors