filter format test with "Empty input format"

tests/src/Kernel/MigrateFilterFormatTest.php

+<?php
+
+namespace Drupal\Tests\migrate_drupal_d5\Kernel;
+
+use Drupal\filter\Entity\FilterFormat;
+use Drupal\filter\FilterFormatInterface;
+
+/**
+ * Migrate filter formats.
+ *
+ * @group migrate_drupal_5
+ */
+class MigrateFilterFormatTest extends MigrateDrupal5TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->executeMigration('d5_filter_format');
+  }
+
+  /**
+   * Test "Empty input format" filter format.
+   */
+  public function testEmptyFilterFormat() {
+    $filter_format = FilterFormat::load('empty_input_format');
+    $this->assertInstanceOf(FilterFormatInterface::class, $filter_format);
+    // Check filter status.
+    $filters = $filter_format->get('filters');
+    $this->assertEmpty($filters);
+  }
+}