Friday, March 1, 2013

How to write Unit Test in Java using JUnit4 in Eclipse and Netbeans

Writing Junit tests for Java classes in Eclipse and Netbeans IDE are super easy, and I will show you with that later in this JUnit tutorial. Before that, let’s revise what is unit test and why should you write them. Unit test is to test smaller unit of code, e.g. methods.  Writing unit test to test individual unit of code is one of the best development practice and helps to find bug earlier in development cycle. Though there are other unit testing framework available in Java e.g. TestNG, JUnit has it’s own place among Java developers. IMHO code review and unit testing are two most important practices for improving code quality and should always be followed during software development. Sad thing is that not every developer follows it; some programmer don’t write unit test due to ignorance and others due to laziness. Any way, it’s just start which take time, once you start writing unit tests, you will automatically start enjoying it. I have seen Java developers testing there code with main() method, but now they prefer to test them with JUnit testcases. I agree few initial tests are difficult because of knowledge and inertia and best way to approach is to start with simplest of JUnit tests. In this JUnit tutorial, I will show you how to write and execute JUnit test from Eclipse and Netbeans, two popular Java IDE. By the way, if you are looking for any good book on JUnit and unit testing, you should look Pragmatic Unit Testing in Java with JUnit, it's an amazing book and teaches a lot about both JUnit and unit testing in Java.


JUnit 3 and JUnit 4 testing framework

JUnit frameworks is popular from quite a sometime now and there are two popular versions available in form of JUnit 3.8, known as JUnit 3 and  JUnit 4. Working of both versions are same, as you create testcases, testsuite and execute them. Main difference between JUnit 4 and JUnit 3 is that, JUnit4 is based on annotation feature of Java 1.5  and easy to write, while JUnit 3 uses “test” keyword, to identify test methods. What is bonus in terms of writing JUnit tests for Java program is that, two of most popular Java IDE, Eclipse and Netbeans has inbuilt support and provides easy interface and infrastructure to create and execute JUnit tests for Java classes. In this JUnit 4 tutorial, we will see step by step guide for writing JUnit test in Eclipse and Netbeans with simple example of Calculator. Our Calculator class has methods add() and multiply() for addition and multiplication, I have used variable arguments of Java 1.5 to implement these methods, so that they can accept any number of parameter.

How to write JUnit tests in Eclipse

1. Create a New Java Project called JUnitExample.
2. Create a Java class Calculator in project which should have add() and multiply() method.
3. Right click on Java class and click on create Junit testcase

How to write JUnit test case in Eclipse JAvaHow to execute JUnit tests in Eclipse

How to run Unit test using Eclipse in JavaNow you have your Junit test created, you can execute it just like you run any Java application:

Right Click --> Run As --> Junit Test

This will run all the JUnit tests declared in this class and will pass if all the test run successfully and pass the condition tested by various assert statement and fail if any of JUnit tests failed. Eclipse will print stack trace and hyper link to the failed test and you can go and fix the problem.

How to write JUnit tests in Netbeans

Junit support in Netbeans is also great and seamless. Here is the steps to create JUnit test in Netbeans

1. Create a New Java Project called JUnitExample.
2. Create a Java Class Calculator in project which should have add() and multiply() method.
3. Now Select a Java Class --> Right click --> Tools --> Create Junit tests
this will create Junit test class for all the methods of selected Java class.

How to execute Junit tests in Netbeans

Executing JUnit tests in Netbeans is much simpler than it was in Eclipse. Go to your Junit test class and right click and select run File option. This will execute all the JUnit tests on File and show the result in console. As earlier test will be pass if all test method passes otherwise it will fail. Netbeans also shows complete stack trace and hyperlink of failed test cases.

Code
Here is complete code example of, How to write unit test in Java using JUnit framework. In this example, we have a Java class called Calculator, which has two methods add() and multiply() and takes variable arguments. In this JUnit tutorial, we will write JUnit testcases, to test these two methods.

/**
 * Simple Java Calculator with add and multiply method
 */
public class Calculator {

        public int add(int... number) {
                int total = 0;
                for (int i : number) {
                        total += i;
                }
                return total;
        }

        public int multiply(int... number) {
                int product = 0;
                for (int i : number) {
                        product *= i;
                }
                return product;
        }

}


Following class CalculatorTest is our JUnit test class, it contains two methods testAdd() and testMultiply(). Since we are using JUnit 4, we don’t need to use prefix test, but I have used that to make test methods explicit. @Test annotation is used by JUnit 4 framework to identify all test cases. If you are new to JUnit 4, then see this post to learn more about JUnit 4 annotations. By the way when we run this class as JUnit Test, it will show how many test cases pass and how many failed. If all the test cases pass then it will show green bar, otherwise red bar to indicate failure.

import static org.junit.Assert.*;
import org.junit.Test;

/**
 * JUnit Test class for testing methods of Calculator class.
 */
public class CalculatorTest {

        @Test
        public void testAdd() {
                Calculator calc = new Calculator();
                assertEquals(60, calc.add(10,20,30));
        }

        @Test
        public void testMultiply() {
                Calculator calc = new Calculator();
                assertEquals(6000, calc.multiply(10,20,30));
        }

}

That’s all on How to write unit test in Java using JUnit framework in Eclipse and Netbeans. JUnit testing framework is is very useful for writing and executing unit test for Java classes and it can also be integrated into build system by using ANT and Maven, which means you can all your tests automatically at build time. By the way since many project have there JUnit test running during build process, it’s good to keep  unit test short and quickly executable to avoid lengthy build. See JUnit best practices guide more unit testing practices. Also start using Junit 4 annotations, they have made job of writing unit tests much easier. 

Recommended Book: Pragmatic Unit Testing in Java with JUnit


8 comments :

Anonymous said...

Very interesting articles, I've read them for a while and I've learned a lot of useful things and tricks.

I think a mistake has slipped into this one; please check the test for multiply method, is calling the add method instead of multiply.

Javin @ Java Classloder Working said...

@Anonymous, good catch :), it should call multiply method, correct now.

Anonymous said...

Testing with main method is not a bad idea either, but yes it doesn't tell whether you test is successful or not, until you use assertion provided by JDK.

Hemanth said...

Not sure if you have intentionally done this to find the error in junit test case, but shouldn't product be initialized to 1 instead of 0 in multiply() method ?

Shailesh Jangra said...

I am looking for a unit test case which tests the program which is written for reading HTML from any website and save it to any file(.txt).
Can you help?

Anonymous said...

How to create suite of Unit test in JUnit 4 verison?

Anonymous said...

Should be this.
0*10*20*30 is still a goddamn zero.

public int multiply(int... number) {
int product = 1;
for (int i : number) {
product *= i;
}
return product;
}

Виктор said...

Right. In multiply must product = 1

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