Why not programatically created nodes in the simpletests?
Here is what the Drupal documentation says on it's simpletest page.


  Testing methodology
  Drupal testing focuses on functional testing
  instead of unit testing. What this means is that the tests are written
  in such a way that they test the interface as a whole instead of
  testing individual functions or finite pieces of code. Drupal focuses
  on functional testing because it is more effective for the way Drupal
  is written. Functional testing ends up being just as effective if not
  more effective than unit testing and especially so due to the code
  style used in Drupal. The testing framework is geared towards this
  type of testing and the documentation focuses on writing functional
  tests.


Drupal tests are almost always functional tests and not unit tests. As quoted above, Drupal was coded in such a way (e.g. hooks system, forms api, etc) that Unit tests generally don't make sense.