Issue #2234771 by tstoeckler: Drupal_get_profile() should not fall back to 'standard'.

core/includes/common.inc

@@ -193,8 +193,10 @@ function drupal_get_region_content($region = NULL, $delimiter = ' ') {
  * installation state. At all other times, the "install_profile" setting will be
  * available in settings.php.
  *
- * @return $profile
- *   The name of the installation profile.
+ * @return string|null $profile
+ *   The name of the installation profile or NULL if no installation profile is
+ *   currently active. This is the case for example during the first steps of
+ *   the installer or during unit tests.
  */
 function drupal_get_profile() {
   global $install_state;
@@ -205,11 +207,12 @@ function drupal_get_profile() {
       $profile = $install_state['parameters']['profile'];
     }
     else {
-      $profile = '';
+      $profile = NULL;
     }
   }
   else {
-    $profile = Settings::get('install_profile') ?: 'standard';
+    // Fall back to NULL, if there is no 'install_profile' setting.
+    $profile = Settings::get('install_profile');
   }
 
   return $profile;

core/modules/simpletest/lib/Drupal/simpletest/Tests/DrupalUnitTestBaseTest.php

@@ -266,4 +266,14 @@ function testEnableModulesTheme() {
     $this->assertTrue(drupal_render($element));
   }
 
+  /**
+   * Tests that drupal_get_profile() returns NULL.
+   *
+   * As the currently active installation profile is used when installing
+   * configuration, for example, this is essential to ensure test isolation.
+   */
+  public function testDrupalGetProfile() {
+    $this->assertNull(drupal_get_profile());
+  }
+
 }