Abstract Class:

public abstract class SampleAbstract {
    public Task newTask;
    public void createT(Id caseId, Id accountId) {

        newTask = new Task();
       
        methodX();
        methodY();

    }
   
    public abstract void methodX();
    public abstract void methodY();

}

Class extending Abstract class:

public class Sample extends SampleAbstract {  
   
    public sample() {
    }
   
    public override void methodX(){
    }
   
    public override void methodY(){
    }  


}

Test class:

@isTest
private class AbstractTest {

    static testMethod void test() {

        Sample sa = new Sample();  
           
        Id caseId;
        Id accountId;
        sa.createT(caseId, accountId);  

    }

}