How to use unit tests to verify the correctness of Java functions?

Java unit testing using JUnit: Install JUnit dependencies. Create a test class with the same name, suffix Test, for each class to be tested. Use @Test to annotate the method to be tested. In the test method, create an instance of the class under test, call the method to be tested, and check the expected results using the assert method. Run the test class to execute the tests.

Use unit testing to verify the correctness of Java functions

Introduction

Unit testing is an important and integral practice in software development, used to verify the expected behavior of software components such as functions or classes. This tutorial will walk you through how to use JUnit for unit testing in Java.

Install JUnit

To install JUnit in your project, use the following Maven dependencies:

 junit junit 4.13.2 test 

Create test class

For each class you want to test, you need to create a test class with the same name, with the suffixTest. For example, for a class namedMyClass, the test class would beMyClassTest.

Annotation method

Use the@Testannotation to mark the method to be tested. Each@Testannotated method is an independent test case.

Example test method

The following example shows a test case for testing theaddmethod:

public class MyClassTest { @Test public void testAdd() { MyClass myClass = new MyClass(); int result = myClass.add(1, 2); assertEquals(3, result); } }

The test above Medium:

• myClassis an instance of the class under test. The
• addmethod is called with the input values1and2.
• resultThe variable stores the value returned by the method.
• assertEqualsThe assertion method checks whether the actual resultresultis equal to the expected result3.

Running Tests

Running a test class from the IDE or command line will execute the test cases. The test will succeed if all assertions pass; otherwise, it will fail.

Practical case

Consider the followingAverageCalculatorclass:

public class AverageCalculator { public double average(int[] numbers) { double sum = 0; for (int number : numbers) { sum += number; } return sum / numbers.length; } }

Supporting test class

public class AverageCalculatorTest { @Test public void testAverage() { AverageCalculator calculator = new AverageCalculator(); double result = calculator.average(new int[]{1, 2, 3, 4}); assertEquals(2.5, result, 0.001); } }

This test case ensures that the calculator correctly calculates the average when given an array of numbers.

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