--- /dev/null
+<?php
+
+namespace Drupal\Tests\Core\Form;
+
+use Drupal\Tests\UnitTestCase;
+use Drupal\Core\Form\OptGroup;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Form\OptGroup
+ * @group Form
+ */
+class OptGroupTest extends UnitTestCase {
+
+ /**
+ * Tests the flattenOptions() method.
+ *
+ * @dataProvider providerTestFlattenOptions
+ */
+ public function testFlattenOptions($options) {
+ $this->assertSame(['foo' => 'foo'], OptGroup::flattenOptions($options));
+ }
+
+ /**
+ * Provides test data for the flattenOptions() method.
+ *
+ * @return array
+ */
+ public function providerTestFlattenOptions() {
+ $object1 = new \stdClass();
+ $object1->option = ['foo' => 'foo'];
+ $object2 = new \stdClass();
+ $object2->option = [['foo' => 'foo'], ['foo' => 'foo']];
+ $object3 = new \stdClass();
+ return [
+ [['foo' => 'foo']],
+ [[['foo' => 'foo']]],
+ [[$object1]],
+ [[$object2]],
+ [[$object1, $object2]],
+ [['foo' => $object3, $object1, ['foo' => 'foo']]],
+ ];
+ }
+
+}