TwigExtensionTestString example

'cache' => FALSE,
      'autoescape' => 'html',
      'optimizations' => 0,
    ]);

    // By default, TwigExtension will attempt to cast objects to strings.     // Ensure objects that implement MarkupInterface are unchanged.     $safe_string = $this->createMock('\Drupal\Component\Render\MarkupInterface');
    $this->assertSame($safe_string, $this->systemUnderTest->escapeFilter($twig, $safe_string, 'html', 'UTF-8', TRUE));

    // Ensure objects that do not implement MarkupInterface are escaped.     $string_object = new TwigExtensionTestString("<script>alert('here');</script>");
    $this->assertSame('&lt;script&gt;alert(&#039;here&#039;);&lt;/script&gt;', $this->systemUnderTest->escapeFilter($twig, $string_object, 'html', 'UTF-8', TRUE));
  }

  /** * @covers ::safeJoin */
  public function testSafeJoin() {
    $this->renderer->expects($this->any())
      ->method('render')
      ->with(['#markup' => '<strong>will be rendered</strong>', '#printed' => FALSE])
      ->willReturn('<strong>will be rendered</strong>');