Updated RUNNING_UNIT_TESTS documentation with mention of the build_da…

…tabases rake tasks.

activerecord/RUNNING_UNIT_TESTS

@@ -31,8 +31,13 @@ That'll run the base suite using the MySQL-Ruby adapter.  Some tests rely on the
 being initialized - you can initialize the schema with:
 
   rake test_mysql TEST=test/cases/aaa_create_tables_test.rb
+  rake mysql:build_databases
+
+To setup the testing environment for PostgreSQL use this command:
+
+  rake postgresql:build_databases
 
 The incantation for running a particular test looks like this
 
-  ruby -w -I"lib:test:test/connections/native_postgresql" test/cases/datatype_test_postgresql.rb -n test_timestamp_with_zone_values_without_rails_time_zone_support
+  rake test TEST=test/cases/datatype_test_postgresql.rb TESTOPTS="-n test_timestamp_with_zone_values_without_rails_time_zone_support"