reactjs - Testing fetch using Jest- React Native -

i have common api class use handling api calls in react native. make call , json/ error , return it. see code below.

// general api acces data web import apiconstants './apiconstants'; export default function api(path,params,method, sssid){      let options;         options = object.assign({headers: {             'accept': 'application/json',             'content-type': 'application/json'         }},{ method: method }, params ? { body: json.stringify(params) } : null );       return fetch(apiconstants.base_url+path, options).then( resp => {         let json = resp.json();         if (resp.ok) {             return json;         }         return json.then(err => {             throw err;         }).then( json => json );     }); } 

but when write jest test mock api folllows in tests folder.

test('should login',() => {     global.fetch = jest.fn(() => new promise((resolve) => {         resolve( { status: 201, json: () => (mock_data_login) });     }));      return api(apiconstants.login,{'un':'test1','pwd':'1234'},'post', null).then((data1)=>{          expect(data1).tobedefined();         expect(data1.success).toequal(true);         expect(data1.message).toequal('login success');     });  }); 

it fails typeerror: json.then not function

when change fetch return this, test passes.

 return fetch(apiconstants.base_url+path, options).then( resp => {             let json = resp.json();             return json         });     } 

why type error error popping up? can't change api module, because redux saga code change. should do?

in code, json object , not promise, undefined. that's complain getting because trying use undefined function. problem not in test in code ha san error. try following instead.

return fetch(apiconstants.base_url+path, options)         .then(resp => resp.json())         .then( json => json)         .catch((error) => error);     });