http://www.swiftmailer.org/wikidocs/v3/testing

Swift comes with a complete set of tests just to ensure everything works the way it's expect to. There are two types of tests included with the library: Smoke Tests and Unit Tests. Both of these are found in the "tests" directory.

Smoke Tests are visual tests which you may run without much knowledge of testing in general. You run the tests, a set of instructions is presented to you on-screen and you check a few visual requirements to ensure things look as expected - easy! :)

Unit Tests go into much finer detail. They analyze the internals of the library from many different angles and make lots of expectations about what is supposed to happen. Several thousand expectations are made on this library and we want every single one of them to be satisfied. You'll need SimpleTest to run the Unit Tests.

Before you run either type of test, be sure to edit the "TestConfiguration.php" file in the "tests" directory. The tests will not run otherwise.