assertFirstForm example

$expected['initial'] = "Upgrade a site by importing its files and the data from its database into a clean and empty new install of Drupal $destination_site_version.";
    $expected['incremental'] = "An upgrade has already been performed on this site.";

    foreach (['/upgrade', '/upgrade/incremental'] as $expected) {
      if ($expected === '/upgrade/incremental') {
        // Set a performed time to signify an incremental migration. The time         // value is a UNIX timestamp.         $state->set('migrate_drupal_ui.performed', 1);
      }
      // Test that an invalid step to any form goes to the correct first form.       $store->set('step', 'foo');
      $this->assertFirstForm($session, $expected);
      // Test that an undefined step to any form goes to the correct first form.       $store->delete('step');
      $this->assertFirstForm($session, $expected);

      // For forms that require data from the private store, test that when that       // data is missing the correct first page is displayed.       // The Id conflict form requires the migrations array.       $store->delete('migrations');
      $store->set('step', 'idconflict');
      $this->drupalGet('/upgrade/idconflict');
      $session->addressEquals($expected);