You can read when running: $ ./Tools/Scripts/test-webkitpy Suppressing most webkitpy logging while running unit tests. Skipping tests in the following modules or packages because they are really, really, slow: webkitpy.common.checkout.scm.scm_unittest (https://bugs.webkit.org/show_bug.cgi?id=31818; use --all to include) ... But bug 31818 was resolved long time ago and running with the "--all" parameter doesn't take that long. Hence, this test should be added back in the list of the default tests to be run.
Although maybe we can wait for bug 143967 to be fixed first.