Debugging and Testing in Dart: Tools and Techniques

Are you tired of spending hours trying to find a bug in your Dart code? Have you ever released a project only to have it crash on the first run? Don't worry, you're not alone! Debugging and testing are essential parts of any project, and Dart offers a variety of tools and techniques to make them easier. In this article, we'll cover some of the best ways to debug and test your Dart code.

Debugging in Dart

Debugging is the process of finding and fixing errors in your code. Dart provides several tools to help you debug your code.


One of the simplest ways to debug your code is to use logging. In Dart, you can use the print() function to log messages to the console. These messages can help you understand what your code is doing and where it might be going wrong. For example, if you're not sure whether a variable is being set correctly, you can use print() to log its value:

var myVariable = "Hello, World!";
print(myVariable); // Outputs "Hello, World!" to the console.

Logging can be a useful tool, but it's important to remember to remove debug statements before deploying your code in production. Otherwise, you risk exposing sensitive information or cluttering your logs.


Another powerful tool for debugging in Dart is breakpoints. Breakpoints allow you to stop the execution of your code at a specific point and inspect the state of your application. You can set breakpoints in your code by clicking on the line number in the editor, or by pressing F9:

Setting a breakpoint in Dart

Once you've set a breakpoint, you can run your code and it will stop at that line. You can then use the debugger to step through your code, inspect variables, and find the source of any issues.


Dart also comes with a set of powerful debugging tools called DevTools. DevTools is a browser-based debugger that allows you to inspect the state of your application, view console output, and much more. To use DevTools, you'll need to install the Dart extension for your browser of choice (Chrome or Firefox).

Once you've installed the extension, you can open DevTools by running your Dart application with the --observe flag:

dart run --observe my_application.dart

This will start your application and open DevTools in your browser. From there, you can inspect network requests, view the call stack, and much more.

Testing in Dart

Testing is the process of verifying that your code works as expected. Dart provides several libraries and tools for testing your applications.

Unit Testing

One of the most common types of testing in Dart is unit testing. Unit tests are tests that verify the behavior of individual units of code, such as functions or classes. Dart provides a built-in testing library called test that makes it easy to write unit tests.

Here's an example of a simple unit test in Dart:

import 'package:test/test.dart';

void main() {
  test('addition', () {
    expect(1 + 1, equals(2));

In this example, we're using the test library to define a test case that verifies that 1 + 1 equals 2.

To run this test, we can use the test package's command-line tool:

dart pub run test

This will run all of the tests in our project and report on their results.


Sometimes, unit tests can be challenging to write because they depend on external services or libraries. A popular solution to this problem is to use mocking. Mocking is the process of creating a fake version of an external service or library for use in your tests.

Dart provides several mocking libraries, including mockito. Here's an example of how to use mockito to mock an HTTP client:

import 'package:http/http.dart' as http;
import 'package:mockito/mockito.dart';

class MockHttpClient extends Mock implements http.Client {}

void main() {
  test('fetchData', () async {
    final client = MockHttpClient();
        .thenAnswer((_) async => http.Response('{"value": 42}', 200));

    final response = await fetchData(client);
    expect(response['value'], equals(42));

In this example, we're creating a mock HTTP client using mockito, and using it to test a function called fetchData. We're also using when() to define what the mock HTTP client should return when it receives a specific request.

Integration Testing

In addition to unit testing, Dart also supports integration testing. Integration testing is the process of testing how different parts of your application work together. Dart provides a library called flutter_test that makes it easy to write integration tests for Flutter applications.

Here's an example of an integration test in Dart:

import 'package:flutter_test/flutter_test.dart';
import 'package:my_app/main.dart' as app;

void main() {
  group('MyApp', () {
    testWidgets('saves a value to storage when button is pressed',
        (WidgetTester tester) async {
      await tester.pumpWidget(app.MyApp());

      await tester.tap(find.byType(ElevatedButton));
      await tester.pump();
      expect('value'), equals('test'));

In this example, we're testing a Flutter application that saves a value to storage when a button is pressed. We're using the testWidgets function from flutter_test to simulate user interactions with the application and verify that the expected result occurs.

Continuous Integration

Finally, it's important to remember that testing is an ongoing process. One way to ensure that your code is always properly tested is to use continuous integration (CI). CI is the process of automatically building and testing your code whenever changes are made.

Dart integrates with several popular CI services, including Travis CI and CircleCI. These services can automatically build and test your code whenever you push changes to your repository, giving you early feedback on any issues that may arise.


Debugging and testing are essential parts of any project, and Dart provides a variety of tools and techniques to make them easier. Whether you're using logging, breakpoints, or debugging tools like DevTools, you can quickly find and fix issues in your code. And with unit tests, mocking, and integration tests, you can be confident that your code is working as expected. By using these tools and techniques, you can ensure that your Dart projects are robust, reliable, and ready for production.

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Written by AI researcher, Haskell Ruska, PhD ( Scientific Journal of AI 2023, Peer Reviewed