i have a batch class as below :
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public class DM_TechAvailability implements Database.Batchable<sObject> {
    public DM_TechAvailability(){
        
    }
    
    public Database.QueryLocator start (Database.BatchableContext BC){
        string BLANK = '';
        string nulll = NULL;
        
        String query = 'select id, SV_Date_String__c, SV_Date__c from SV_Technician_Availability__c 
        where SV_Date__c  != null and (SV_Date_String__c =: BLANK or SV_Date_String__c =: nulll)';
        
        system.debug('1*'+Database.getQueryLocator(query));
        return Database.getQueryLocator(query);
    }
    public void execute(Database.BatchableContext BC, List<sObject> xTcope){
        List<SV_Technician_Availability__c> taList = new List<SV_Technician_Availability__c>();
        for(sObject eachTcope: xTcope){
            SV_Technician_Availability__c eachTA = (SV_Technician_Availability__c)eachTcope;
            eachTA.SV_Date_String__c = String.ValueOf(eachTA.SV_Date__c);
            taList.add(eachTA);
        }
        Database.update(taList, false);
    }
    public void finish(Database.BatchableContext Bc){
        
    }

}

Test Class which i have written as :
-----------------------------------------------
@isTest
public class Test_DM_TechAvailibility {

    @isTest
    public static void Test_method() {
        
        List<SV_Technician_Availability__c> techAvailabilityList = new List<SV_Technician_Availability__c>();
        for(Integer i=0; i<10; i++) {
            SV_Technician_Availability__c techAv = new SV_Technician_Availability__c();
            techAv.SV_Date_String__c = '';
            techAv.SV_Date__c = System.Today();
            techAvailabilityList.add(techAv);            
        }
        insert techAvailabilityList;
        
        system.debug('2*'+techAvailabilityList);
        
        test.startTest();
            DM_TechAvailability obj = new DM_TechAvailability();
            Database.executeBatch(obj);
        test.stopTest();
    }         
        
}

It covers only 50% and doesn't cover 'Execute' method of apex class.
Can you please help with your inputs how can i increase the percentage?

Thanks in Advance !
Rupesh