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Dart – Unit Testing

Last Updated : 09 May, 2021
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Unit Testing is a process of testing individual components of a software/application separately, to ensure that each component is functioning as intended. 

It provides multiple advantages such as –

  • Ability to test out individual components without running the whole software/application.
  • Pinpoint errors easily inside a specific component.

Dart provides a package called test which lets the developer carry out unit testing very easily. In this article, we’ll write a few unit tests using this package, demonstrating various use cases and results.

Setting up the Project:

Since we’re using test, which is an external dart package, a separate project has to be created to run the project.

We’ve to create a pubspec.yaml file, and add the following lines to the project.

name: DartTesting


Then we’ve to run the following command

dart pub get

This will initialize a project with the name DartTesting and also install the test package as a dev dependency

Next, we can create a main.dart file which will contain all our code and import the test package there.

import 'package:test/test.dart';

Writing a Sample Function:

First, we’ve to write a simple function on which we can run our tests. Provided below is the code for calculating the sum of all the elements of an array.


// Get sum of all elements of an array
int getSumOfArray(List<int> arr) {
  int res = 0;
  for (var i=0; i<arr.length; i++) {
    res += arr[i];
  return res;

Writing a Unit Test:

A unit test can be written for the above function by using the test() function. It takes in 2 Arguments

  1. A string value containing a description of the unit test
  2. A test assertion by using the expect() function. The expect() function has to be provided with 2 values:
    • Expected Value, which is provided manually by the developer.
    • Actual Value, which is obtained by running the concerned function
    • If these values match, then the Unit Test is successful, or else it is considered to be failing.

Provided below is the code for a unit test for getSumOfArray() function. Since the expected and actual values match, it’ll be a successful test.


main() {
  // Successful test for sum of array
  test('Get sum of array - success', () {
    int expectedValue = 15;
    int actualValue = getSumOfArray([1, 2, 3, 4, 5]);
    expect(expectedValue, actualValue);


00:00 +0: Get sum of array - success

00:00 +1: All tests passed!


Handling Failing Tests:

In this case, the expected value is different from the actual value, due to which the test will fail.


main() {
  // Unsuccessful test for sum of array
  test('Get sum of array - failure', () {
    int expectedValue = 40;
    int actualValue = getSumOfArray([1, 2, 3, 4, 5]);
    expect(expectedValue, actualValue);


00:00 +0: Get sum of array - failure

00:00 +0 -1: Get sum of array - failure [E]

  Expected: <15>
    Actual: <40>

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