Added info on how to run rake with different database adapters

railties/guides/source/contributing_to_rails.textile

@@ -72,7 +72,16 @@ mysql> GRANT ALL PRIVILEGES ON activerecord_unittest2.*
 
 If you’re using another database, check the files under +activerecord/test/connections+ in the Rails source code for default connection information. You can edit these files if you _must_ on your machine to provide different credentials, but obviously you should not push any such changes back to Rails.
 
-Now if you go back to the root of the Rails source on your machine and run +rake+ with no parameters, you should see every test in all of the Rails components pass. After that, check out the file +activerecord/RUNNING_UNIT_TESTS+ for information on running more targeted database tests, or the file +ci/ci_build.rb+ to see the test suite that the Rails continuous integration server runs.
+Now if you go back to the root of the Rails source on your machine and run +rake+ with no parameters, you should see every test in all of the Rails components pass. If you want to run the all ActiveRecord tests (or just a single one) with another database adapter, enter this from the +activerecord+ directory:
+
+<shell>
+rake test_sqlite3 
+rake test_sqlite3 TEST=test/cases/validations_test.rb
+</shell>
+
+You can change +sqlite3+ with +jdbcmysql+, +jdbcsqlite3+, +jdbcpostgresql+, +mysql+ or +postgresql+. Check out the file +activerecord/RUNNING_UNIT_TESTS+ for information on running more targeted database tests, or the file +ci/ci_build.rb+ to see the test suite that the Rails continuous integration server runs.
+
+
 
 NOTE: If you're working with Active Record code, you _must_ ensure that the tests pass for at least MySQL, PostgreSQL, SQLite 2, and SQLite 3. Subtle differences between the various Active Record database adapters have been behind the rejection of many patches that looked OK when tested only against MySQL.