I don't have a problem with shipping the full test suite with the module. In the event of failures that cannot be explained through other means, then having the user run the test suite in there environment and feed the results back to the author makes good sense. But running the test suite on every installation doesn't.
Shipping a test suite that I, as a user of the module, can inspect and run to verify that things are just peachy-keen with all the scary internals of some CPAN module makes me very happy.
In most cases, I don't have the time or desire to read every line of a module, but I do have enough time to skim the tests and make sure that there's test coverage for the main functionality I need. Or, if not, that I can easily add that coverage before writing code that depends on that functionality.
Without the full test suite, that's much harder. And, should I find it necessary to make local changes to the module, a full test suite makes it much, much easier to be confident that a) I didn't break something, and b) that if it looks like the change might be generally usefu, that it could be submitted back to the maintainer without causing him/her all sorts of grief trying to debug it.