diff -u b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
--- b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Definition of Drupal\system\Tests\Theme\ThemeTest.
+ * Contains Drupal\system\Tests\Theme\ThemeTestTwig.
  */
 
 namespace Drupal\system\Tests\Theme;
@@ -10,7 +10,7 @@
 use Drupal\simpletest\WebTestBase;
 
 /**
- * Tests low-level theme functions.
+ * Tests theme functions with the Twig engine.
  */
 class ThemeTestTwig extends WebTestBase {
 
@@ -82,4 +82,7 @@
     $this->drupalGet('theme-test/template-test');
-    $this->assertRaw('<p id="null-test">null: </p>', t('NULL values render as empty strings in Twig templates.'));
+    foreach (_test_theme_twig_php_values() as $type => $value) {
+      $this->assertRaw('<li>' . $type . ': ' . $value['expected'] . '</li>');
+    }
   }
+
 }
diff -u b/core/modules/system/tests/themes/test_theme_twig/test_theme_twig.theme b/core/modules/system/tests/themes/test_theme_twig/test_theme_twig.theme
--- b/core/modules/system/tests/themes/test_theme_twig/test_theme_twig.theme
+++ b/core/modules/system/tests/themes/test_theme_twig/test_theme_twig.theme
@@ -1,4 +1,5 @@
 <?php
+use Drupal\system\Tests\Theme\ThemeTestTwig;
 /**
  * @file
  * Theme to help test the Twig engine.
@@ -10,12 +11,3 @@
 function test_theme_twig_preprocess_theme_test_template_test(&$variables) {
-  // Build an array of type => value pairs for testTwigVariableDataTypes().
-  $types = array(
-    'null' => NULL,
-  );
-
-  foreach ($types as $type => $value) {
-    // Prefix each variable with "twig_" so that twig doesn't get confused
-    // between a variable and a primitive.
-    $variables['twig_' . $type] = $value;
-  }
+  $variables['php_values'] = _test_theme_twig_php_values();
 }
diff -u b/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.html.twig b/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.html.twig
--- b/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.html.twig
+++ b/core/modules/system/tests/themes/test_theme_twig/theme_test.template_test.html.twig
@@ -4 +4,5 @@
-<p id="null-test">null: {{ twig_null }}</p>
+<ul>
+{% for key, php_value in php_values %}
+  <li>{{ key }}: {{ php_value.value }}</li>
+{% endfor %}
+</ul>
\ No newline at end of file
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/theme_test/theme_test.module
+++ b/core/modules/system/tests/modules/theme_test/theme_test.module
@@ -172,3 +172,41 @@ function theme_theme_test_foo($variables) {
   return $variables['foo'];
 }
 
+/*
+ * Helper function to test PHP variables in the Twig engine.
+ */
+function _test_theme_twig_php_values() {
+  // Prefix each variable with "twig_" so that twig doesn't get confused
+  // between a variable and a primitive. Arrays are not tested since they should
+  // be a Drupal render array.
+  return array(
+    'twig_null' => array(
+      'value' => NULL,
+      'expected' => '',
+    ),
+    'twig_bool_false' => array(
+      'value' => FALSE,
+      'expected' => '',
+    ),
+    'twig_bool_true' => array(
+      'value' => TRUE,
+      'expected' => '1',
+    ),
+    'twig_int' => array(
+      'value' => 1,
+      'expected' => '1',
+    ),
+    'twig_int_0' => array(
+      'value' => 0,
+      'expected' => '0',
+    ),
+    'twig_float' => array(
+      'value' => 122.34343,
+      'expected' => '122.34343',
+    ),
+    'twig_string' => array(
+      'value' => 'Hello world!',
+      'expected' => 'Hello world!',
+    ),
+  );
+}