Memory leaks on Drupal 6.x while running tests with simpletest

Hello everyone,

I was trying to get simpletest test running on a Drupal 6.x installation with drush 4.5. I've downloaded and installed the simpletest module with drush and applied the simpletest/D6-core-simpletest.patch patch to Drupal core. I've also applied the patch mentioned here because drush was throwing the same error described in this bug report.

When running the test suite, it happens that some of them exhaust al memory ressources on my test machine (Screenshot of htop and free -m).I've increased the available system memory to ~2,5GB and some tests still fail because a lack of memory. Some of the failing tests are:

drush --root='/var/www' --uri='http://localhost/' test-run FileFieldDisplayTestCase --no-all --backend 
drush --root='/var/www' --uri='http://localhost/' test-run ImageFieldDisplayTestCase --no-all --backend
drush --root='/var/www' --uri='http://localhost/' test-run ImageFieldValidateTestCase --no-all --backend

I was using the test runner with this command line: drush --uri='http://localhost/' test-run --all --xml

While running the whole test suite, I've also noticed, that the host process also seems to leak some memory: After running for about half an hour, the host process uses almost a Gigabyte of memory.

Is there some way to fix this?