Hii,
 I am Writing a test class for  cotroller but it is not getting  pass , it is always throwing error in the controller part as"DML Exception".
This is my extension class 
 

public CPCommAttachCls(ApexPages.StandardController stdController) {
        
        objId = ApexPages.currentPage().getParameters().get('CaseID');
        objCaseRec = [select CaseNumber, Subject from case where case.id =: objId];
        caseNumber = objCaseRec.CaseNumber;
        subject = objCaseRec.Subject;
       
       // initializing caseComment
       comment = new CaseComment();
       comment.parentid=objid;
        
      // initializing the variable for Attachment process
      CaseAttachment = new Attachment(); 
      CaseAttachment.parentId=objid; 
        
    }      // Controller scope finished

And this is my test class for passing the controller

@isTest(SeeAllData=true)
public class CPCommAttachTestCls {
    public static TestMethod void Testclass()
    {  
    //  CaseComment comment = new CaseComment();
      Case c = Cse();
      ApexPages.StandardController sc = new ApexPages.StandardController(c);
      CpCommAttachCls ContCls = new CpCommAttachCls(sc); // This line giving error
      
        
    }
    static Case cse(){
    Case c = new Case();
    c.subject = 'LogMeIn Pro2';
    c.Description='Test Description';
    c.General_App_Area__c='A';
    c.Priority='High';
    c.Status='New';
    insert c;
    return c;
}

}

I am using the standard controller case. But it is giving me error.