errors in database.mysqli.inc in line 134

While I'm running simpletest with simpletest_clone i get error messages in database.mysqli.inc in line 134 like:
Table 'a.b_simpletest9758system' doesn't exist query: SELECT name, filename, throttle FROM b_simpletest9758system WHERE type = 'module' AND status = 1 ORDER BY weight ASC, filename ASC

or

Table 'a.b_simpletest9758semaphore' doesn't exist query: SELECT expire, value FROM b_simpletest9758semaphore WHERE name = 'menu_rebuild'
etc.

or

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') ORDER BY fit DESC LIMIT 0, 1' at line 1 query: SELECT * FROM b_simpletest673920menu_router WHERE path IN () ORDER BY fit DESC LIMIT 0, 1

I had a look at similar issues on the net. I found that these are related to incorrect istallation of drupal: empty database or similar especially during updating to newer versions.

What is this? How can I solve this?

This is the structure of my test file:

class ABC extends SimpleTestCloneTestCase {

 public static function getInfo() {
  return array(
   'name' => t('aaa'),
   'description' => t('bbb.'),
   'group' => t('ccc'),
  );
 }

 function setUp() {
  parent::setUp();
 }

 function tearDown() {
  parent::tearDown();
 }

 function testDEF() {
  $this->drupalLogin((object)array('name' => 'username', 'pass_raw' => 'pwd'));
  $this->drupalLogout();
 }


}