API testing in Flutter

It is very common to use API in our Flutter projects. Testing makes the Flutter project very easy to maintain, in this way you will save a lot of debugging time. Also when you have testing in place you can always check whether API working as expected. 

Let’s create a simple API endpoint in PHP in our local server. If you don’t anything about PHP web development, It’s quite fun to work in PHP. This PHP file just responds with a JSON which has a list of Books, nothing complex right? 

Server:

<?php

$b1 = ['title' => 'Beginning App Development with Flutter', 'author' => 'Rap Payne'];
$b2 = ['title' => 'Beginning Flutter: A Hands On Guide to App Development', 'author' => 'Marco L. Napoli'];
$b2 = ['title' => 'Flutter Apprentice', 'author' => 'Vincenzo Guzzi, Kevin D Moore, Vincent Ngo and Michael Katz'];

$books = [$b1, $b2];

header("content-type: application/json; charset=UTF-8");
echo json_encode($books, JSON_PRETTY_PRINT);

[
    {
        "title": "Beginning App Development with Flutter",
        "author": "Rap Payne"
    },
    {
        "title": "Flutter Apprentice",
        "author": "Vincenzo Guzzi, Kevin D Moore, Vincent Ngo and Michael Katz"
    }
]

Flutter:

Let’s first create a flutter project called “api_test”, we will use VSCode for the rest of the project.

flutter create api_test

Let’s add http package by this command, run on your terminal.

flutter pub add http

Go to your lib folder and create two files model.dart and service.dart.

Model: 

On the model.dart creates a book class.

class Book {
  final String title;
  final String author;

  Book({required this.title, required this.author});
}

API:

In the service, class create an abstract class like this 

abstract class BookApi {
import 'package:api_test/model.dart';
import 'package:http/http.dart' as http;
import 'dart:convert' as convert;

abstract class BookApi {
  Future<List<Book>> books();
}

class BookService implements BookApi {
  Future<List<Book>> books() async {
    var url = Uri.parse('http://localhost/flutter/book.php');
    var response = await http.get(url);

    //print(response.body);
    if (response.statusCode == 200) {
      final listResponse = convert.jsonDecode(response.body) as List;
      List<Book> books = listResponse
          .map(
            (e) => Book(
              title: e['title'],
              author: e['author'],
            ),
          )
          .toList();
      return books;
    } else {
      print('Request failed with status: ${response.statusCode}.');
      return [];
    }
  }
}

create another class in the same file for the above BookApi method implementation

Test:

Create a test file called book_service_test.dart in test folder

import 'package:api_test/model.dart';
import 'package:api_test/service.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  var book_service = BookService();

  test('book api', () async {
    final result = await book_service.books();
    print(" test $result");

    expect(result.isNotEmpty, true);
    expect(result, isA<List<Book>>());
  });
}

Our tests are passed when the list is not empty and list has a book type.

Download the full source code