Issue #2347511 by davidhernandez, lauriii, rpayanm, kasn: Add method to test if class attribute has class on Attribute object.

core/lib/Drupal/Core/Template/Attribute.php

@@ -188,6 +188,24 @@ class Attribute implements \ArrayAccess, \IteratorAggregate {
     return $this;
   }
 
+  /**
+   * Checks if the class array has the given CSS class.
+   *
+   * @param string $class
+   *   The CSS class to check for.
+   *
+   * @return bool
+   *   Returns TRUE if the class exists, or FALSE otherwise.
+   */
+  public function hasClass($class) {
+    if (isset($this->storage['class']) && $this->storage['class'] instanceOf AttributeArray) {
+      return in_array($class, $this->storage['class']->value());
+    }
+    else {
+      return FALSE;
+    }
+  }
+
   /**
    * Implements the magic __toString() method.
    */

core/tests/Drupal/Tests/Core/Template/AttributeTest.php

@@ -140,6 +140,21 @@ class AttributeTest extends UnitTestCase {
     $this->assertEmpty((string) $attribute);
   }
 
+  /**
+   * Tests checking for class names with the Attribute method.
+   * @covers ::hasClass()
+   */
+  public function testHasClass() {
+    // Test an attribute without any classes.
+    $attribute = new Attribute();
+    $this->assertFalse($attribute->hasClass('a-class-nowhere-to-be-found'));
+
+    // Add a class to check for.
+    $attribute->addClass('we-totally-have-this-class');
+    // Check that this class exists.
+    $this->assertTrue($attribute->hasClass('we-totally-have-this-class'));
+  }
+
   /**
    * Tests removing class attributes with the Attribute helper methods.
    * @covers ::removeClass()