JSON parsing in flutter

I'm working with flutter application.I fetch demo json file dummy JSON file using this URL fetching JSON value.but when I try by adding json file created in the assets folder and file directory path I added in the code. but it's not working and in pubspec.yaml file I added like this

assets: - assets/test.json.

import 'package:flutter/services.dart' show rootBundle;

Future<Map> _loadAStudentAsset() async { return await rootBundle.loadString('assets/test.json'); }

What I'm doing wrong here. Can anyone suggest me? How to work with json file which is present in the same project folder. And feel free to tell is there any mistakes in my code. Here is my working code.

import 'dart:async';
import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:intl/intl.dart';

 Map data;
 List features; // features object list
void main() async {
data = await getQuakes();

features = data['features'];

 //print(_data['features'][0]['properties']);

 runApp(new MaterialApp(
   title: 'Quakes',
   home: new Quakes(),
  ));
}

class Quakes extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return new Scaffold(
       appBar: new AppBar(
        title: new Text('Quakes'),
        centerTitle: true,
        backgroundColor: Colors.red,
       ),
  body: new Center(
    child: new ListView.builder(
        itemCount: features.length,
        padding: const EdgeInsets.all(15.0),
        itemBuilder: (BuildContext context, int position) {
          //crating the rows for our listview
          if (position.isOdd) return new Divider();
          final index = position ~/
              2; // we are dividing position by 2 and returning an integer result

          var format = new DateFormat.yMMMMd("en_US").add_jm();
          //var dateString = format.format(date);
          var date = format.format(new DateTime.fromMicrosecondsSinceEpoch(
              features[index]['properties']['time'] * 1000,
              isUtc: true));

          return new ListTile(
            title: new Text(
              " $date",
              //title: new Text("Date: $date",
              style: new TextStyle(
                  fontSize: 15.5,
                  color: Colors.orange,
                  fontWeight: FontWeight.w500),
            ),
            subtitle: new Text(
              "${_features[index]['properties']['place']}",
              style: new TextStyle(
                  fontSize: 14.5,
                  fontWeight: FontWeight.normal,
                  color: Colors.grey,
                  fontStyle: FontStyle.italic),
            ),
            leading: new CircleAvatar(
              backgroundColor: Colors.green,
              child: new Text(
                "${_features[index]['properties']['mag']}",
                style: new TextStyle(
                    fontSize: 16.5,
                    fontWeight: FontWeight.bold,
                    color: Colors.white,
                    fontStyle: FontStyle.normal),
              ),
            ),
            onTap: () {
              showAlertMessage(
                  context, "${_features[index]['properties']['title']}");
            },
          );
        }),
  ),
);
}

   void _showAlertMessage(BuildContext context, String message) {
      var alert = new AlertDialog(
      title: new Text('Quakes'),
      content: new Text(message),
      actions: <Widget>[
           new FlatButton(
             onPressed: () {
                Navigator.pop(context);
             },
           child: new Text('OK'))
      ],
     );
  showDialog(context: context, builder: (context) => alert);
 }
}

Future<Map> getQuakes() async {
 String apiUrl = 
 'https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_day.geojson';

   http.Response response = await http.get(apiUrl);

   return json.decode(response.body);
 }