The other way to run tests without loading the entire Rails framework is to write tests that don’t require the entire Rails framework.
That sounds crazy, I know, since we’re writing a Rails application. Bear with me.
The tests we’ve written so far mostly fall into five groups:
End-to-end tests. These tests require the entire Rails stack since we’re testing the entire stack.
Tests that use only ActiveRecord and need the database. Right now this group includes tests for ActiveRecord finder methods, and our action object tests that save to the database.
Controller tests that require ActionPack and may or may not require ActiveRecord and may or may not touch the database.
Tests that use ActiveRecord objects ...