diff --git a/tests/src/Template/TwigExtensionTest.php b/tests/src/Template/TwigExtensionTest.php
new file mode 100644
index 0000000..7bb5f05
--- /dev/null
+++ b/tests/src/Template/TwigExtensionTest.php
@@ -0,0 +1,74 @@
+<?php
+
+namespace Drupal\Tests\components\Template;
+
+use Drupal\components\Template\TwigExtension;
+use Drupal\Core\Template\Loader\StringLoader;
+use Drupal\Tests\PhpunitCompatibilityTrait;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\components\Template\TwigExtension
+ * @group components
+ */
+class TwigExtensionTest extends UnitTestCase {
+
+  /**
+   * The renderer.
+   *
+   * @var \Drupal\Core\Render\RendererInterface|\PHPUnit_Framework_MockObject_MockObject
+   */
+  protected $renderer;
+
+  /**
+   * The system under test.
+   *
+   * @var \Drupal\Core\Template\TwigExtension
+   */
+  protected $systemUnderTest;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+    $this->renderer = PhpunitCompatibilityTrait::createMock('\Drupal\Core\Render\RendererInterface');
+
+    $this->systemUnderTest = new TwigExtension($this->renderer);
+  }
+
+  /**
+   * Tests creating #theme render arrays within a Twig template.
+   *
+   * @covers ::theme
+   */
+  public function testTheme() {
+    $loader = new StringLoader();
+    $twig = new \Twig_Environment($loader);
+    $twig->addExtension($this->systemUnderTest);
+
+    $result = $twig->render(
+      '{{ theme("item_list", { "items": list }) }}',
+      [
+        'list' => ['this', 'list'],
+      ]
+    );
+    $expected = '<ul><li>this</li><li>list</li></ul>';
+    $this->assertEquals($expected, $result);
+
+    // Test nested render array.
+    $result = $twig->render(
+      '{{ theme("item_list", { "items": [ link ] }) }}',
+      [
+        'link' => [
+          '#type' => 'link',
+          '#title' => 'example link',
+          '#url' => 'https://example.com',
+        ],
+      ]
+    );
+    $expected = '<ul><li><a href="https://example.com">example link</a></li></ul>';
+    $this->assertEquals($expected, $result);
+  }
+
+}