Deletes created files, database tables, and reverts all environment changes.
This method needs to be invoked for both unit and integration tests.
Overrides DrupalUnitTestBase::tearDown
TestBase::prepareDatabasePrefix()
TestBase::changeDatabasePrefix()
TestBase::prepareEnvironment()
public function tearDown() {
$this->fixtures
->dropTables(Database::getConnection());
parent::tearDown();
}