file: common.inc.test:

...

class valid_email_address_TestCase extends DrupalTestCase {
  function testValidEmailExample() {
    $this->assertTrue(valid_email_address("admin@example.com"));
  }

  function testInvalidEmailNoDomain() {
    $this->assertFalse(valid_email_address("admin@"));
  }

  ...
}

class t_TestCase extends DrupalTestCase {
  function testPlainStringNoSubstitution() {
    $string = 'Plain string';
    $this->assertEquals($string, t($string));
  }

  function testStringWithCheckPlainPlaceholder() {
    $string = 'String with @placeholder';
    $this->assertEquals('String with monkey', t($string, array('@placeholder' => 'monkey'));
  }

  ...
}

...