reactjs - How to test assignment lines in saga function using jest -

i have function consists of saga effect calls want coverage full function out missing line of code how can test if condition here

export function* fetchfromsource() { const datatypename = mapdatatypes(datatype);       iif (datatypename.length === 0) {         return;       }       yield put(sourceactions.onrdsmsourceplantrequeststarted()); } 

how test datatypename.length using jest this mapdatatypes unit test method

it('should return appropriate datatype when mapdatatypes triggered', () => {       const expected = 'items';       const actiondatatype = action.payload.name;       expect(expected).toequal(saga.mapdatatypes(actiondatatype));     }); 

this next put test method

it('should return onrdsmsourceplantrequeststarted action', () => {       const expectedaction = {         type: 'rdsm/sourceview/on_rdsm_source_plant_request_started',       };       const datatypename = '';       const gennext = generator.next(datatypename);       expect(gennext.value).toequal(put(expectedaction));     }); 

here test passing verify put call without entering if block. my question how verify if block

probably should change implementation of saga, , make mapdatatypes call declarative: const datatypename = yield call(mapdatatypes, datatype). can test this:

it('should end saga when there no datatypename', () => {   const datatypename = '';   expect(generator.next().value).toequal(call(mapdatatypes, datatype));   expect(generator.next(datatypename).done).tobetruthy(); });  it('should return onrdsmsourceplantrequeststarted action', () => {   const expectedaction = {     type: 'rdsm/sourceview/on_rdsm_source_plant_request_started',   };   const datatypename = 'something';   expect(generator.next().value).toequal(call(mapdatatypes, datatype));   expect(generator.next(datatypename).value).toequal(put(expectedaction)); });