Apex Trigger to move Attachment from Task to Parent

AttachtoParent.trg

//
// Author : M Hamza Siddiqui
// Created Date : 9/14/2018
// Description : Apex Trigger to move Attachment from Task to Parent Object Record (on the basis of WHATID i.e. RelatedTo)
//
// Initializing Trigger when any new attachment get inserted in SF
trigger AttachtoParent on Attachment (after insert) {
    List<Attachment> Attachments = new list<Attachment>();
    // Looping thorugh the attachments
    for (Attachment a : trigger.new){
    	Attachments.add(a);
    }
    
    if(Attachments !=null && Attachments.size() > 0 ){
    	AttachtoParent_Handler att = new AttachtoParent_Handler(Attachments);
    }

}

AttachtoParent_Handler.apxc

public class AttachtoParent_Handler {
	
    public AttachtoParent_Handler(List<Attachment> Attach){
        if(Attach != null && Attach.size() > 0){
            for (Attachment a : Attach){
                String parentIdString = String.valueof(a.parentId);
                // Making sure if the attachment is from the Task
                if (parentIdString.substring(0,3) == '00T'){
                    // Getting Parent Object Id
                    task parent = [SELECT Id,WhatId FROM Task WHERE Id = :a.parentId]; 
                    if (parent.WhatId  != null){
                        Attachment body = [SELECT Body FROM Attachment WHERE Id = :a.Id];
                        // Adding same attachment to Parent Object Record Id.
                        Attachment newA = New Attachment(
                            Name = a.Name,
                            Body = body.Body,
                            OwnerId = a.OwnerId,
                            ParentId = parent.WhatId
                        );
                        insert newA;
                    }
                }
            }
    	}	
    }
}

AttachtoParent_Handler_Test.apxc

@isTest
public class AttachtoParent_Handler_Test {

    static testMethod void testAttachments()
    {
      Task task=new Task();
      insert task;

      Attachment attach=new Attachment();   	
      attach.Name='Unit Test Attachment';
      Blob bodyBlob=Blob.valueOf('Unit Test Attachment Body');
      attach.body=bodyBlob;
      attach.parentId=task.id;
      insert attach;
    	
    	List<Attachment> attachments=[select id, name from Attachment where parentId=:task.Whatd];
    	System.assertEquals(1, attachments.size());
    }
}