How to use Dart test()
The test() function in Dart allows developers to define test cases, make assertions, and validate the expected behavior of their code. It is a powerful tool for ensuring code correctness.
This function plays a crucial role in software development by verifying the smallest testable software units, such as functions, methods, or classes. In the image below, different type of testing is displayed.
Implementation
We can follow the instructions given below to implement the test() function.
Install the test package by defining it into pubspec.yaml file.
Import the package into the dart file.
Define the test cases according to the syntax guidelines.
Installing the package
To begin using the test() function in Dart, we need to install the necessary package that provides the testing framework. For this purpose, we will open the pubspec.yaml in our dart project and will add the following line under the "dependencies" section.
dependencies
test:
After making the changes, we can install the package in two ways.
Right-click the
pubspec.yamlfile and click on "get packages."Write the following command in the terminal.
dart pub get
Importing the package
We can import a package into the Dart file by adding the following line of code in the Dart file where we want to implement the test() function:
import "package:test/test.dart";
Syntax
We can specify tests in Dart using test(), while the expect() functions.
test("Here we can write description of the test", () {
// Here you can specify any variable or logic
expect(actualValue , expectedOutcome)
});
We can also group multiple tests using a group() function and specify a group description for it.
group("We can specify group name here", () {
test("Here we can write description of the test 1", () {
expect(actual, exptected);
});
test("Here we can write description of the test 2", () {
expect(actual, expected);
});
})
Code examples
Here we will discuss two examples by putting together the code explained above, one where test cases will be passed and the other where some will fail.
Passing test case
In the code below, we have two files: index.dart, where one test case is defined, and the other is pubspec.yaml file where the test package is declared so we can import it into the dart file.
// Import the test package
import "package:test/test.dart";
// Function to be tested
int Add(int x,int y) {
var z = x+y;
return z;
}
void main() {
print(" ");
// Define the test
test("test to check add method",(){
// Arrange
var expected = 30;
// Act
var actual = Add(10,20);
// Asset
expect(actual,expected);
});
}Code Explanation
Lines 5–8: This code defines a
Add()function, which is being tested, takes two integers as input parameters, adds them together, and returns the sum.Lines 13–22: A test case is defined using the
test()function. The test case has a description("test to check add method"). Inside the test case, a variableexpectedis initialized with the expected sum value. TheAdd()function is invoked with input values (10 and 20), and the result is stored in theactualvariable. Theexpect()function is used to compare theactualandexpectedvalues. If they match, the test case passes; otherwise, it fails.
Output
As the index.dart contains only one test case, and it passed, so the output shows +1 in the final output.
00:00 +0: test to check add method
00:00 +1: All tests passed!
Failing test case
In the code below, we again have the same two files index.dart, where two test cases are defined but they are grouped, and the other is pubspec.yaml file where the test package is declared so we can import it into the dart file.
// Import the test package
import 'package:test/test.dart';
// Function to be tested
int Add(int x,int y){
return x+y;
}
int Sub(int x,int y){
return x-y-1;
}
void main(){
group("This is a group",(){
test('test to check sub',(){
var expected = 10;
// Arrange
var actual = Sub(30,20);
// Act
expect(actual,expected);
// Assert
});
test("test to check add method",(){
var expected = 30;
// Arrange
var actual = Add(10,20);
// Act
expect(actual,expected);
// Asset
});
});
}Code Explanation
Lines 5–10: Two functions are defined for the test:
Add()andSub().Add()takes two parametersxandy, and returns their sum whileSub()subtractsyfromxand then subtracts1from the result.Line 14: A test block is defined using the
group()function. It groups related tests and provide a description.Lines 15–34: We have two individual test cases defined using the
test()function in the test group. The first test, 'test to check sub,' checks the result of theSub()function and expects the value10as the outcome. The second test, 'test to check add method,' checks the result of theAdd()function and expects the value30as the outcome.
Output
This time index.dart file contains two test cases, but as a group, one fails, and the other passes, so the count becomes +1 -1.
00:00 +0: This is a group test to check sub
00:00 +0 -1: This is a group test to check sub [E]
Expected: <10>
Actual: <9>
package:matcher/src/expect/expect.dart 149 fail
package:matcher/src/expect/expect.dart 144 _expect
package:matcher/src/expect/expect.dart 56 expect
index.dart 22 main.<fn>.<fn>
package:test_api/src/backend/declarer.dart 215 Declarer.test.<fn>.<fn>
===== asynchronous gap ===========================
package:test_api/src/backend/declarer.dart 213 Declarer.test.<fn>
===== asynchronous gap ===========================
package:test_api/src/backend/invoker.dart 258 Invoker._waitForOutstandingCallbacks.<fn>
00:00 +0 -1: This is a group test to check add method
00:00 +1 -1: Some tests failed.
Conclusion
The Dart test() function is essential for ensuring code quality. Developers can effectively implement tests verifying their software units' correctness by installing the test package, importing it into their Dart files, and following the syntax guidelines. This practice helps catch potential bugs and ensures the code behaves as expected. Adopting a test-driven development approach with test() in Dart can lead to more reliable applications.
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