diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index d00f819..0d935ae 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -355,7 +355,7 @@ function drupal_environment_initialize() {
     if (!drupal_valid_http_host($_SERVER['HTTP_HOST'])) {
       // HTTP_HOST is invalid, e.g. if containing slashes it may be an attack.
       header($_SERVER['SERVER_PROTOCOL'] . ' 400 Bad Request');
-      exit;
+      return false;
     }
   }
   else {
@@ -1454,7 +1454,7 @@ function drupal_handle_request($test_only = FALSE) {
   // Exit if we should be in a test environment but aren't.
   if ($test_only && !drupal_valid_test_ua()) {
     header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
-    exit;
+    return false;
   }
 
   $kernel = new DrupalKernel('prod', drupal_classloader(), !$test_only);
@@ -1658,7 +1658,7 @@ function _drupal_bootstrap_page_cache() {
       // We are done.
       $response->prepare($request);
       $response->send();
-      exit;
+      return false;
     }
     else {
       drupal_add_http_header('X-Drupal-Cache', 'MISS');
@@ -1813,7 +1813,7 @@ function drupal_valid_test_ua($new_prefix = NULL) {
     $key_file = DRUPAL_ROOT . '/sites/simpletest/' . substr($prefix, 10) . '/.htkey';
     if (!is_readable($key_file)) {
       header($_SERVER['SERVER_PROTOCOL'] . ' 403 Forbidden');
-      exit;
+      return false;
     }
     $private_key = file_get_contents($key_file);
     // The file properties add more entropy not easily accessible to others.
diff --git a/core/includes/errors.inc b/core/includes/errors.inc
index 05937ff..68b66a6 100644
--- a/core/includes/errors.inc
+++ b/core/includes/errors.inc
@@ -167,7 +167,7 @@ function _drupal_log_error($error, $fatal = FALSE) {
       // When called from CLI, simply output a plain text message.
       // Should not translate the string to avoid errors producing more errors.
       print html_entity_decode(strip_tags(format_string('%type: !message in %function (line %line of %file).', $error))). "\n";
-      exit;
+      return false;
     }
   }
 
@@ -178,7 +178,7 @@ function _drupal_log_error($error, $fatal = FALSE) {
         // Should not translate the string to avoid errors producing more errors.
         print format_string('%type: !message in %function (line %line of %file).', $error);
       }
-      exit;
+      return false;
     }
   }
   else {
@@ -240,7 +240,7 @@ function _drupal_log_error($error, $fatal = FALSE) {
       $response->setStatusCode(500, '500 Service unavailable (with message)');
       // An exception must halt script execution.
       $response->send();
-      exit;
+      return false;
     }
   }
 }
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index b00d23b..5853b83 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -285,7 +285,7 @@ function install_begin_request(&$install_state) {
   // installation be permitted using such a prefix.
   if ($install_state['interactive'] && strpos($request->server->get('HTTP_USER_AGENT'), 'simpletest') !== FALSE && !drupal_valid_test_ua()) {
     header($request->server->get('SERVER_PROTOCOL') . ' 403 Forbidden');
-    exit;
+    return false;
   }
 
   drupal_bootstrap(DRUPAL_BOOTSTRAP_CONFIGURATION);
@@ -548,7 +548,7 @@ function install_run_task($task, &$install_state) {
         \Drupal::service('session_manager')->save();
         // Send the response.
         $response->send();
-        exit;
+        return false;
       }
     }
     // If we are in the middle of processing this batch, keep sending back
@@ -922,7 +922,7 @@ function install_display_output($output, $install_state) {
   }
 
   print DefaultHtmlPageRenderer::renderPage($output, $output['#title'], 'install', $regions);
-  exit;
+  return false;
 }
 
 /**
diff --git a/core/install.php b/core/install.php
index 156ff91..7a0a383 100644
--- a/core/install.php
+++ b/core/install.php
@@ -23,7 +23,7 @@
 // load that file yet as it would cause a fatal error on older versions of PHP.
 if (version_compare(PHP_VERSION, '5.4.2') < 0) {
   print 'Your PHP installation is too old. Drupal requires at least PHP 5.4.2. See the <a href="http://drupal.org/requirements">system requirements</a> page for more information.';
-  exit;
+  return false;
 }
 
 // Start the installer.
diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index 9de9815..135fc08 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -265,7 +265,7 @@ public function buildForm($form_id, array &$form_state) {
     // If the form returns some kind of response, deliver it.
     if ($response instanceof Response) {
       $this->sendResponse($response);
-      exit;
+      return false;
     }
 
     // If this was a successful submission of a single-step form or the last step
@@ -510,7 +510,7 @@ public function retrieveForm($form_id, &$form_state) {
     // If the form returns some kind of response, deliver it.
     if ($form instanceof Response) {
       $this->sendResponse($form);
-      exit;
+      return false;
     }
     $form['#form_id'] = $form_id;
 
diff --git a/core/modules/system/tests/modules/form_test/form_test.module b/core/modules/system/tests/modules/form_test/form_test.module
index 42ef667..5a1b064 100644
--- a/core/modules/system/tests/modules/form_test/form_test.module
+++ b/core/modules/system/tests/modules/form_test/form_test.module
@@ -34,7 +34,7 @@ function _form_test_submit_values_json($form, &$form_state) {
   $response = new JsonResponse($form_state['values']);
   // @todo remove once converted to new routing system.
   $response->send();
-  exit;
+  return false;
 }
 
 /**
@@ -766,7 +766,7 @@ function form_test_form_state_values_clean_form_submit($form, &$form_state) {
   // This won't have a proper JSON header, but Drupal doesn't check for that
   // anyway so this is fine until it's replaced with a JsonResponse.
   print Json::encode($form_state['values']);
-  exit;
+  return false;
 }
 
 /**
@@ -795,7 +795,7 @@ function form_test_form_state_values_clean_advanced_form($form, &$form_state) {
 function form_test_form_state_values_clean_advanced_form_submit($form, &$form_state) {
   form_state_values_clean($form_state);
   print t('You WIN!');
-  exit;
+  return false;
 }
 
 /**
diff --git a/core/modules/system/tests/modules/session_test/session_test.module b/core/modules/system/tests/modules/session_test/session_test.module
index c618bab..faf57a8 100644
--- a/core/modules/system/tests/modules/session_test/session_test.module
+++ b/core/modules/system/tests/modules/session_test/session_test.module
@@ -7,7 +7,7 @@ function session_test_user_login($account) {
   if ($account->getUsername() == 'session_test_user') {
     // Exit so we can verify that the session was regenerated
     // before hook_user_login() was called.
-    exit;
+    return false;
   }
 }
 
diff --git a/core/modules/toolbar/toolbar.module b/core/modules/toolbar/toolbar.module
index 0f58cb2..7c0670f 100644
--- a/core/modules/toolbar/toolbar.module
+++ b/core/modules/toolbar/toolbar.module
@@ -131,7 +131,7 @@ function _toolbar_initialize_page_cache() {
     $response->prepare($request);
     $response->send();
     // We are done.
-    exit;
+    return false;
   }
 
   // Otherwise, create a new page response (that will be cached).
diff --git a/core/scripts/drupal.sh b/core/scripts/drupal.sh
index 9514341..0fe3079 100755
--- a/core/scripts/drupal.sh
+++ b/core/scripts/drupal.sh
@@ -53,7 +53,7 @@
   ./scripts/{$script}
 \n
 EOF;
-  exit;
+  return false;
 }
 
 // define default settings
diff --git a/core/scripts/password-hash.sh b/core/scripts/password-hash.sh
index f80d75c..8b03e10 100755
--- a/core/scripts/password-hash.sh
+++ b/core/scripts/password-hash.sh
@@ -25,7 +25,7 @@
        PHP version {$version}.
 \n
 EOF;
-  exit;
+  return false;
 }
 
 $script = basename(array_shift($_SERVER['argv']));
@@ -50,7 +50,7 @@
 
 
 EOF;
-  exit;
+  return false;
 }
 
 // Password list to be processed.
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 3134a5c..03a00c3 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -22,7 +22,7 @@
 
 if ($args['help'] || $count == 0) {
   simpletest_script_help();
-  exit;
+  return false;
 }
 
 simpletest_script_init();
@@ -32,7 +32,7 @@
   simpletest_script_setup_database();
   simpletest_script_run_one_test($args['test-id'], $args['execute-test']);
   // Sub-process exited already; this is just for clarity.
-  exit;
+  return false;
 }
 
 simpletest_script_setup_database(TRUE);
@@ -47,7 +47,7 @@
   foreach ($messages['status'] as $text) {
     echo " - " . $text . "\n";
   }
-  exit;
+  return false;
 }
 
 if ($args['list']) {
@@ -61,7 +61,7 @@
       echo " - " . $info['name'] . ' (' . $class . ')' . "\n";
     }
   }
-  exit;
+  return false;
 }
 
 $test_list = simpletest_script_get_test_list();
@@ -92,7 +92,7 @@
 }
 
 // Test complete, exit.
-exit;
+return false;
 
 /**
  * Print help text.
@@ -265,7 +265,7 @@ function simpletest_script_parse_args() {
       else {
         // Argument not found in list.
         simpletest_script_print_error("Unknown argument '$arg'.");
-        exit;
+        return false;
       }
     }
     else {
@@ -278,7 +278,7 @@ function simpletest_script_parse_args() {
   // Validate the concurrency argument
   if (!is_numeric($args['concurrency']) || $args['concurrency'] <= 0) {
     simpletest_script_print_error("--concurrency must be a strictly positive integer.");
-    exit;
+    return false;
   }
 
   return array($args, $count);
@@ -604,7 +604,7 @@ function simpletest_script_execute_batch($test_classes) {
 
       if (!is_resource($process)) {
         echo "Unable to fork test process. Aborting.\n";
-        exit;
+        return false;
       }
 
       // Register our new child.
@@ -852,7 +852,7 @@ function simpletest_script_get_test_list() {
       foreach ($args['test_names'] as $file) {
         if (!file_exists($file)) {
           simpletest_script_print_error('File not found: ' . $file);
-          exit;
+          return false;
         }
         $content = file_get_contents($file);
         // Extract a potential namespace.
@@ -886,7 +886,7 @@ function simpletest_script_get_test_list() {
 
   if (empty($test_list)) {
     simpletest_script_print_error('No valid tests were specified.');
-    exit;
+    return false;
   }
   return $test_list;
 }
diff --git a/core/scripts/update-countries.sh b/core/scripts/update-countries.sh
index eee5fa2..1571964 100755
--- a/core/scripts/update-countries.sh
+++ b/core/scripts/update-countries.sh
@@ -78,7 +78,7 @@ function t($string) {
 }
 if (empty($countries)) {
   echo 'ERROR: Did not find expected country names.' . PHP_EOL;
-  exit;
+  return false;
 }
 // Sort by country code (to minimize diffs).
 ksort($countries);
diff --git a/core/update.php b/core/update.php
index 3bac378..9e10ab3 100644
--- a/core/update.php
+++ b/core/update.php
@@ -33,7 +33,7 @@
 // load that file yet as it would cause a fatal error on older versions of PHP.
 if (version_compare(PHP_VERSION, '5.4.2') < 0) {
   print 'Your PHP installation is too old. Drupal requires at least PHP 5.4.2. See the <a href="http://drupal.org/requirements">system requirements</a> page for more information.';
-  exit;
+  return false;
 }
 
 /**
@@ -317,7 +317,7 @@ function update_task_list($active = NULL) {
   $system_schema = db_query('SELECT schema_version FROM {system} WHERE name = :system', array(':system' => 'system'))->fetchField();
   if ($system_schema < \Drupal::CORE_MINIMUM_SCHEMA_VERSION) {
     print 'Your system schema version is ' . $system_schema . '. Updating directly from a schema version prior to 8000 is not supported. You must <a href="https://drupal.org/node/2179269">migrate your site to Drupal 8</a> first.';
-    exit;
+    return false;
   }
 }