Test suite does not detect changes in schema

1. Configure test_config.php for dbal testing.
2. Run the test suite.
3. Alter phpbb schema, e.g. add a table called phpbb_ext.
4. Run the test suite.

The test suite now fails with the following errors:

41) phpbb_extension_manager_test::test_available
PHPUnit_Extensions_Database_Operation_Exception: COMPOSITE[TRUNCATE] operation failed on query:
TRUNCATE "phpbb_ext"
using args: Array
(
)
[SQLSTATE[42P01]: Undefined table: 7 ERROR: relation "phpbb_ext" does not exist]

I also get:

40) phpbb_dbal_db_tools_test::test_create_index_against_index_exists
SQL ERROR [ postgres ]<br /><br />ERROR: relation "prefix_table_name_seq" already exists []<br /><br />An sql error occurred while fetching this page. Please contact an administrator if this problem persists.

Not sure how it manages to produce both of these errors in the same test run.

The test suite remains broken until I clear out the database manually (did it by dropping and recreating).