Unit Testing in Dart

Typing testing ensures that your app keeps working as you add more features or change existing functionality. Unit testing helps to confirm the behavior of a single function, method, or class. The test package provides a basic test unit framework.

Software testing, which is an important part of app development, helps to make sure your app is running properly before you release it for deployment. This Dart test guide outlines several types of tests, and identifies where you can learn to test Flutter, web, and server side applications and scripts.

You can run tests on the command line using the dart test command ( or, with Flutter applications, flutter testing ).

Kinds of testing

Dart test documents focus on three types of tests, the many types of tests you may be familiar with are ' Unit ', ' Component ', and ' end-to-end ' ( a form of integration testing ). Test terms vary, but here are some of the principles and concepts you may encounter when using Dart technology :

Unit Tests

Unit testing is focused on verifying a small piece of testable software, such as a function, method, or category. Your test suites should have more test units than other test types.

Component Tests

The component test ( called Flutter widget test ) ensures that the component ( which usually includes multiple classes ) behaves in the expected manner. Partial testing often requires the use of artificial materials that can mimic user actions, events, create structure, and strengthen child parts.

Integration and end-to-end Tests

The final integration and testing ensure the behavior of the entire application, or a large part of the application. Integration testing usually comes on a modified or real device or browser ( web ) and consists of two pieces: the app itself, and the test application that puts the app in motion. Integration tests usually measure performance, so the test application usually works on a different device or OS rather than the test application.

Generally useful libraries

The tests that you perform partly depend on the platform your code is intended for—Flutter, the web, or server-side, for example — the following packages are useful across Dart platforms :

1. package : test

Provides a standard way of writing tests in Dart. You can use the test package to:

1. Write single tests, or groups of tests.
2. Use the ‘ @TestOn ’ annotation to restrict tests to run on specific environments.
3. Write asynchronous tests just as you would write synchronous tests.
4. Tag tests using the ‘ @Tag ’ annotation. For example, define a tag to create a custom configuration for some tests, or to identify some tests as needing more time to complete.
5. Create a dart_test.yaml file to configure tagged tests across multiple files or an entire package.

2. Package : mockito

It provides a way to create artificial, easy-to-use objects in fixed environments, and to ensure that the test system interacts with the artificial in the expected ways. An example that uses both package : test and package : mockito, see the International Space Station API library and its unit testing in the mockito package.

Flutter testing

Use the following resources to learn more about testing Flutter apps :

• Testing Flutter Apps :

This teaches how to perform unit, widget, or integration tests on a Flutter app.

• flutter_test :

  This is a testing library for Flutter built on top of ‘ package : test ’.

• flutter_driver :

  This is a testing library for testing Flutter applications on real devices and emulators ( in a separate process ).

• flutter_gallery :

   Source code and tests for the Flutter gallery example.

• flutter/dev/manual_tests :

   Many examples of tests in the Flutter SDK.

Other tools and resources

You may also find the following resources helpful in developing and refining Dart programs.

IDE

When it comes to debugging, your first line of defense is your IDE. Dart plugins are available in most widely used IDEs.

Dart DevTools

Dart DevTools is a Dart and Flutter operating suite. For details, see the Dart DevTools documentation.

Advantages

There are several benefits of using Dart Unit Testing. Some of them are as follows :

1. It provides the capability to test each individual components without running the whole application or software.
2. It easily pinpoints the errors inside each specific component.

Let us dive into the setting up of unit testing :

Setting up of Project

Since Dart ‘ test ’ is an external package of Dart language, we need to create a separate project to run the project.

Create a pubsec.yaml file and write the following code in the project :

name: DartTesting
dev_dependencies:
test:

After that run the following command :

dart pub get 

The next important step is to create a main.dart file which is going to contain the main code of our project. Import the Dart test package in the code to use its functionality.

import ‘package:test/test.dart’ ;

How to write a Unit Test?         

A unit test is written inside any function of the code by using the ‘ test( ) ’ function. This function mainly takes 2 arguments :

1. First Argument : A string value that contains the description of the unit test.
2. Second Argument : Writing the test assertion by using the ‘ except( ) ’ function. This function is provided with the following two values :
   • Expected Value : This value is provided by the developer, manually.
   • Actual Value : This value is obtained by running the concerned function.
   • If the above two values match, then only the Unit Test is successful or else it is considered to be failing.