diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index 80563ef..80a7b5a 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -2444,6 +2444,23 @@ function drupal_get_bootstrap_phase() {
 }
 
 /**
+ * Returns whether a simpletest is running or peparing to run.
+ *
+ * @param $set
+ *   Set whether a test is running.
+ *
+ * @return
+ *   TRUE if test is running, false otherwise.
+ */
+function drupal_test_running($set = NULL) {
+  static $test_running = NULL;
+  if (isset($set)) {
+    $test_running = $set;
+  }
+  return isset($test_running) ? $test_running : (bool)drupal_valid_test_ua();
+}
+
+/**
  * Returns the test prefix if this is an internal request from SimpleTest.
  *
  * @return
diff --git a/includes/common.inc b/includes/common.inc
index 31923f2..b722db2 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -5363,7 +5363,7 @@ function drupal_system_listing($mask, $directory, $key = 'name', $min_depth = 1)
   // For SimpleTest to be able to test modules packaged together with a
   // distribution we need to include the profile of the parent site (in which
   // test runs are triggered).
-  if (drupal_valid_test_ua()) {
+  if (drupal_test_running()) {
     $testing_profile = variable_get('simpletest_parent_profile', FALSE);
     if ($testing_profile && $testing_profile != $profile) {
       $profiles[] = $testing_profile;
diff --git a/modules/simpletest/drupal_web_test_case.php b/modules/simpletest/drupal_web_test_case.php
index 0853c7d..74acb13 100644
--- a/modules/simpletest/drupal_web_test_case.php
+++ b/modules/simpletest/drupal_web_test_case.php
@@ -1419,6 +1419,8 @@ class DrupalWebTestCase extends DrupalTestCase {
     if (!$this->setupEnvironment) {
       return FALSE;
     }
+    // Indicate a test is preparing/running.
+    drupal_test_running(TRUE);
 
     // Reset all statics and variables to perform tests in a clean environment.
     $conf = array();