how to write test class for service resource skill object in field service lightning?Below is my code

    //creating a ServiceResource
        ServiceResource objServiceResource=new ServiceResource();
        objServiceResource.Name='Test Resource';
        objServiceResource.RelatedRecordId=u.Id;
        objServiceResource.ResourceType='T';
        objServiceResource.IsActive=True;
        objServiceResource.Status_Code__c='SB';
        insert objServiceResource;       
 //creating a ServiceResourceSkill
objServiceResourceSkill.ServiceResourceId=objServiceResource.Id;
        objServiceResourceSkill.SkillId=-------;
        objServiceResourceSkill.EffectiveStartDate=System.today();
        objServiceResourceSkill.EffectiveEndDate=System.today();
        insert objServiceResourceSkill;

this is the test obj i have created.I am unable to understand how to give 'SkillId' for the ServiceResourceSkill 
Can any one please help me.
Thankyou,
Muneeswar