public function testGraphIsNotWritableAfterInitializing()
{
$op1 = new GenericOperation(1);
$op2 = new GenericOperation(2);
$op3 = new GenericOperation(3);
$op4 = new GenericOperation(4);
$dm = new DependencyManager();
$dm->addOperation($op1);
$dm->addOperation($op2);
$dm->addOperation($op3);
$dm->addOperation($op4);
$dm->addDependencyByOperation($op1, $op2);
$dm->addDependencyByOperation($op1, $op3);
$dm->addDependencyByOperation($op2, $op4);
$dm->addDependencyByOperation($op3, $op4);
$dm->getExecutableOperations();
$this->setExpectedException('MikeRoetgers\\DependencyGraph\\Exception\\GraphWriteException');
$dm->addDependencyByOperation($op1, $op4);
}
