[BridgeImplementationTest] Add test for "required" attribute on lists and checkboxes

Lists and checkboxes don't support the "required" flag and should not
define it. Note that the "required" flag can be set to false if so
desired.

tests/BridgeImplementationTest.php

@@ -98,6 +98,19 @@ class BridgeImplementationTest extends TestCase {
 
 				if (isset($options['required'])) {
 					$this->assertInternalType('bool', $options['required'], $field . ': invalid required');
+
+					if($options['required'] === true && isset($options['type'])) {
+						switch($options['type']) {
+							case 'list':
+							case 'checkbox':
+								$this->assertArrayNotHasKey(
+									'required',
+									$options,
+									$field . ': "required" attribute not supported for ' . $options['type']
+								);
+								break;
+						}
+					}
 				}
 
 				if (isset($options['title'])) {