Hi Hoysala,
Firstly you have to add the finish method in your batch class.
Follow this batch class:

global class DS_CallsStatusUpdate implements Database.Batchable<sObject>
{
    global Database.queryLocator start(Database.BatchableContext bc)
    {
        return Database.getQueryLocator('SELECT Id,OCE_Account__c,OCE_CallDateTime__c,OCE_Status__c FROM OCE_Call__c WHERE OCE_Status__c =\'draft\' AND OCE_CallDateTime__c<LAST_N_DAYS:2');
    }
    global void execute(Database.BatchableContext bc, List<OCE_Call__c> scope)
    {
        List<OCE_Call__c> callLst = new List<OCE_Call__c>();
        for(OCE_Call__c ca : scope)
        {
            ca.OCE_Status__c = 'Submitted';
            callLst.add(ca);
        }   
        system.debug('calls--'+callLst);
        UPDATE callLst;
    }
    global void finish(Database.BatchableContext BC){
        
    }
}
Test Class:
@isTest
private class DS_CallsStatusUpdate_Test {
    @isTest static void testDS_CallsStatusUpdate() {
        OCE_Call__c obj = new OCE_Call__c();
        obj.Name = 'Test';
        obj.OCE_Account__c = 'TestAccount';
        //If OCE_Account__c is a lookup field
        //then create a record of that Object and put the id as below.
        // obj.OCE_Account__c = Field.Id;
        Obj.OCE_CallDateTime__c = DateTime.newInstance(2019,05,5);
        obj.OCE_Status__c = 'draft';
        insert obj;
 
        Test.startTest();

            DS_CallsStatusUpdate o = new DS_CallsStatusUpdate();
            DataBase.executeBatch(o);
            
        Test.stopTest();
    }
}

I hope you find the above solution helpful. If it does, please mark as Best Answer to help others too.
Thanks,
Ajay Dubedi