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JUNIT - BASIC USAGE


Let us now have a basic example to demonstrate the step-by-step process of using Junit.

Create a Class

Create a java junit class to be tested, say, MessageUtil.java junit in C:\> JUNIT_WORKSPACE

/*
* 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 String printMessage(){
System.out.println(message);
return message;
}
}

Create Test Case Class
  1. Create a java junit test class, say, TestJunit.java junit.
  2. Add a test method testPrintMessage() to your test class.
  3. Add an Annotaion @Test to method testPrintMessage().
  4. Implement the test condition and check the condition using assertEquals API of Junit.
Create a java junit class file name TestJunit.java junit in C:\>JUNIT_WORKSPACE.

import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class TestJunit {
String message = "Hello World";
MessageUtil messageUtil = new MessageUtil(message);
@Test
public void testPrintMessage() {
assertEquals(message,messageUtil.printMessage());
}
}

Create Test Runner Class
  1. Create a TestRunner java junit class.
  2. Use runClasses method of JUnitCore class of JUnit to run the test case of the above created test class.
  3. Get the result of test cases run in Result Object.
  4. Get failure(s) using the getFailures() method of Result object.
  5. Get Success result using the wasSuccessful() method of Result object.
Create a java junit class file named TestRunner.java junit 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 java junitc.

C:\JUNIT_WORKSPACE>java junitc MessageUtil.java junit TestJunit.java junit TestRunner.java junit

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

C:\JUNIT_WORKSPACE>java junit TestRunner

Verify the output.

Hello World
true

Now update TestJunit in C:\>JUNIT_WORKSPACE so that the test fails. Change the message string.

import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class TestJunit {
String message = "Hello World";
MessageUtil messageUtil = new MessageUtil(message);
@Test
public void testPrintMessage() {
message = "New Word";
assertEquals(message,messageUtil.printMessage());
}
}

Let's keep the rest of the classes as is, and try to run the same Test Runner.

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());
}
}

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

C:\JUNIT_WORKSPACE>java junit TestRunner

Verify the output.

Hello World
testPrintMessage(TestJunit): expected:<[New Wor]d> but was:<[Hello Worl]d>
false
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