Sets up unit test environment.
Unlike Drupal\simpletest\WebTestBase::setUp(), UnitTestBase::setUp() does not install modules because tests are performed without accessing the database. Any required files must be explicitly included by the child class setUp() method.
Overrides UnitTestBase::setUp
public function setUp() {
$this->cachebackends = array();
$this->defaultValue = $this
->randomName(10);
parent::setUp();
$this
->setUpCacheBackend();
}