Issue #3251817 by alexpott, jonathan1055, nicxvan, longwave: Make run-tests.sh...

Issue #3251817 by alexpott, jonathan1055, nicxvan, longwave: Make run-tests.sh select all the required tests when testgroups: has more than one value

(cherry picked from commit c7e78f42)

core/scripts/run-tests.sh

@@ -984,11 +984,12 @@ function simpletest_script_get_test_list() {
         simpletest_script_print_alternatives($first_group, $all_groups);
         exit(SIMPLETEST_SCRIPT_EXIT_FAILURE);
       }
-      // Ensure our list of tests contains only one entry for each test.
+      // Merge the tests from the groups together.
       foreach ($args['test_names'] as $group_name) {
-        $test_list = array_merge($test_list, array_flip(array_keys($groups[$group_name])));
+        $test_list = array_merge($test_list, array_keys($groups[$group_name]));
       }
-      $test_list = array_flip($test_list);
+      // Ensure our list of tests contains only one entry for each test.
+      $test_list = array_unique($test_list);
     }
   }