Here is the class where i need unit test

public class extCtrlEx {

private final account acc;
public extCtrlEx(ApexPages.StandardController controller) {
this.acc=(account)controller.getRecord();
}
public string getGreetings(){
return 'Hello '+acc.name ;
}
public void display(){}

}

I tried unit test it populates error like Compile Error: Constructor not defined: [extCtrlEx].() plz help to resolve the issue.

@isTest

public class extCtrlEx_TC

{

static testMethod void testMthd()
{
Account acc=new Account();

// extCtrlEx ece=new extCtrlEx ();

// ece.display();

// ece.getGreetings();

}

}