JUnit - Exceptions Test

JUnit provides an option of tracing the exception handling of code. You can test whether the code throws a desired exception or not. The expected parameter is used along with @Test annotation. Let us see @Test(expected) in action.

Create a Class

Create a java class to be tested, say, MessageUtil.java in C:\> JUNIT_WORKSPACE.
Add an error condition inside the printMessage() method.

/*
* This class prints the given message on console.
*/

public class MessageUtil {

   private String message;

   //Constructor
   //@param message to be printed
   public MessageUtil(String message){
      this.message = message; 
   }

   // prints the message
   public void printMessage(){
      System.out.println(message);
      int a = 0;
      int b = 1/a;
   }   

   // add "Hi!" to the message
   public String salutationMessage(){
      message = "Hi!" + message;
      System.out.println(message);
      return message;
   }   
}   

Create Test Case Class

Create a java test class called TestJunit.java. Add an expected exception ArithmeticException to the testPrintMessage() test case.
Create a java class file named TestJunit.java in C:\>JUNIT_WORKSPACE.

import org.junit.Test;
import org.junit.Ignore;
import static org.junit.Assert.assertEquals;

public class TestJunit {

   String message = "Robert"; 
   MessageUtil messageUtil = new MessageUtil(message);
   
   @Test(expected = ArithmeticException.class)
   public void testPrintMessage() { 
      System.out.println("Inside testPrintMessage()");     
      messageUtil.printMessage();     
   }

   @Test
   public void testSalutationMessage() {
      System.out.println("Inside testSalutationMessage()");
      message = "Hi!" + "Robert";
      assertEquals(message,messageUtil.salutationMessage());
   }
}

Create Test Runner Class

Create a java class file named TestRunner.java in C:\>JUNIT_WORKSPACE to execute test case(s).

import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

public class TestRunner {
   public static void main(String[] args) {
      Result result = JUnitCore.runClasses(TestJunit.class);
  
      for (Failure failure : result.getFailures()) {
         System.out.println(failure.toString());
      }
  
      System.out.println(result.wasSuccessful());
   }
}   

Compile the MessageUtil, Test case and Test Runner classes using javac.

C:\JUNIT_WORKSPACE>javac MessageUtil.java TestJunit.java TestRunner.java

Now run the Test Runner, which will run the test cases defined in the provided Test Case class.

C:\JUNIT_WORKSPACE>java TestRunner

Verify the output. testPrintMessage() test case will be passed.

Inside testPrintMessage()
Robert
Inside testSalutationMessage()
Hi!Robert
true