Simpletest Class, File, and Namespace structure

NOTE: As of Drupal 8 simpletest is deprecated, please use phpunit tests, see https://www.drupal.org/docs/8/phpunit

In Drupal 8, Simpletest tests have to have a specific namespace, file, and class structure in order to be recognized by the testing framework.

Tests of Core functionality

Tests for code under core/lib/Drupal/Component should be done using PHPUnit, not SimpleTest. These classes do not depend on Drupalisms (hooks, etc.), the Drupal database, or even having a Drupal site instantiated. See https://www.drupal.org/phpunit for information.

Tests for code under core/lib/Drupal/Core can be done with SimpleTest, although if possible, PHPUnit tests with mock inputs are preferred. If you are writing a Simpletest test for one of these classes, treat it as if it was a test for the System module.

Tests of Modules

Simpletest tests for any module belong in the \Drupal\(modulename)\Tests namespace, and therefore (following the PSR-4 file convention for PHP classes), they go in .php files under (module directory)/src/Tests. These can be organized into sub-directories if desired. For example, the core System module is in core/modules/system, so its Simpletest tests are in subdirectories of core/modules/system/src/Tests.

Here's an example of one of these test files (core/modules/system/src/Tests/Pager/PagerTest.php, showing just the essential parts of the file and minus the actual test code):

/**
 * @file
 * Contains \Drupal\system\Tests\Pager\PagerTest.
 */

namespace Drupal\system\Tests\Pager;

use Drupal\simpletest\WebTestBase;

/**
 * Tests pager functionality.
 *
 * @group Pager
 */
class PagerTest extends WebTestBase {

  /**
   * Modules to enable.
   *
   * @var array
   */
  public static $modules = array('dblog', 'pager_test');

  /**
   * Tests markup and CSS classes of pager links.
   */
  public function testActiveClass() {
    // Any public method whose name starts with "test" is a test that will be executed.
  }

}

Notes:

• Extend WebTestBase for tests that require a browser.
• $modules gives a list of the modules to enable for the test.
• The @group line in the class doc block tells what group in the Testing module UI the test will appear in. [The @group annotations are really important]
• The first line of the class doc block gives the description of the test that will appear in the Testing module UI