Invoking Drupal core tests from within a custom module .test script
So... I found a solution that's working, at least for my case.

It has to do with the fact that test cases are actually PHP classes that can be extended. So I tried to leverage inheritance, with a caveat...

I want to run a test on the pager, Drupal 7, after I have enabled a module that replaces the core pager.

The core pager test class is defined as 

class PagerFunctionalWebTestCase extends DrupalWebTestCase {


now, my problem was that the core test would not be caring about my module to be loaded before running the tests. 

I created my module test class as an extension of the core one, like

class MyPagerTest extends PagerFunctionalWebTestCase {


This is OK, but the point is that if I call parent::setUp() at this stage, the core setup will be run and I will still miss my module from loading before the actual test.

So the caveat is that instead of calling parent::setUp, I will call directly the 'ancestor' DrupalWebtestCase::setUp function, with my setup, and skip the call to parent.

Like this:

...

public function setUp() {
  // Enable required modules.
  $modules = array(
    'dblog',
    'mypager',
  );
  DrupalWebTestCase::setUp($modules);

  // Insert 300 log messages.
  for ($i = 0; $i &lt; 300; $i++) {
    watchdog('pager_test', $this-&gt;randomString(), NULL, WATCHDOG_DEBUG);
  }

  $this-&gt;admin_user = $this-&gt;drupalCreateUser(array(
    'access site reports',
  ));
  $this-&gt;drupalLogin($this-&gt;admin_user); 

}

....


That's all - class inheritance will do the magic and bring the rest of the test functions in.

Anybody sees other options?