Beef up test fixtures documentation for test/test_helper.rb

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2801 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

railties/helpers/test_helper.rb

@@ -3,11 +3,26 @@ require File.expand_path(File.dirname(__FILE__) + "/../config/environment")
 require 'test_help'
 
 class Test::Unit::TestCase
-  # Turn off transactional fixtures if you're working with MyISAM tables in MySQL
+  # Transactional fixtures accelerate your tests by wrapping each test method
+  # in a transaction that's rolled back on completion.  This ensures that the
+  # test database remains unchanged so your fixtures don't have to be reloaded
+  # between every test method.  Fewer database queries means faster tests.
+  #
+  # Read Mike Clark's excellent walkthrough at
+  #   http://clarkware.com/cgi/blosxom/2005/10/24#Rails10FastTesting
+  #
+  # Every Active Record database supports transactions except MyISAM tables
+  # in MySQL.  Turn off transactional fixtures in this case; however, if you
+  # don't care one way or the other, switching from MyISAM to InnoDB tables
+  # is recommended.
   self.use_transactional_fixtures = true
-  
+
-  # Instantiated fixtures are slow, but give you @david where you otherwise would need people(:david)
+  # Instantiated fixtures are slow, but give you @david where otherwise you
+  # would need people(:david).  If you don't want to migrate your existing
+  # test cases which use the @david style and don't mind the speed hit (each
+  # instantiated fixtures translates to a database query per test method),
+  # then set this back to true.
   self.use_instantiated_fixtures  = false
 
   # Add more helper methods to be used by all tests here...
-end
+end