The following test cases remain to be written:
 Handlers:
  All handlers
 
 Rollback:
  Various options
  
 Import:
  Various options
  Various update scenarios

 Sources:
  Highwater support
  
 Destinations:
  All term fields - presence/absence, default values, boundary conditions, error
    conditions
  All user fields - ditto
  All node fields - ditto
  All comment fields - ditto
  Path module support
  TableCopy destination
  
 Infrastructure:
  Team stuff

The following are features we would like to test, but are (or seem) impractical:
 Drush commands
 SQL Server support