Fix "Could not find table 'users'" during tests

Setting the RAILS_ENV to test ensures that the Rails test setup happens
as expected, loading the schema into the test database before the tests
are run. This fixes a problem where the tests would fail with this
message if `bundle exec rake test` is run on a fresh checkout:

    ActiveRecord::StatementInvalid:  Could not find table 'users'

Author: mattbrictson

test/test_helper.rb

@@ -1,3 +1,5 @@
+ENV['RAILS_ENV'] ||= 'test'
+
 require 'timecop'
 require 'diffy'
 require 'nokogiri'