assertTeapotHeaders example

// Test ['#attached']['http_header] = ['Status', $code].     $this->drupalGet('/render_attached_test/teapot');
    $this->assertSession()->statusCodeEquals(418);
    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'MISS');
    // Repeat for the cache.     $this->drupalGet('/render_attached_test/teapot');
    $this->assertSession()->statusCodeEquals(418);
    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'HIT');

    // Test ['#attached']['http_header'] with various replacement rules.     $this->drupalGet('/render_attached_test/header');
    $this->assertTeapotHeaders();
    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'MISS');
    // Repeat for the cache.     $this->drupalGet('/render_attached_test/header');
    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'HIT');

    // Test ['#attached']['feed'].     $this->drupalGet('/render_attached_test/feed');
    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'MISS');
    $this->assertFeed();
    // Repeat for the cache.     $this->drupalGet('/render_attached_test/feed');