Create an administrator account within Drupal 7 SimpleTest.

create-administrator-account.php

<?php

class TrashTestCase extends DrupalWebTestCase {

  # [...]

  public function testAdminContentNodesList() {
    # Administrator account
    $permissions = module_invoke_all('permission');
    $permissions = array_keys($permissions);
    $account     = $this->drupalCreateUser($permissions);
    # [...]
  }

}