Let us have a basic example to demonstrate the step-by-step process of using JUnit.
1. Create a Class :-
Create a java class to be tested, say, MessageUtil.java 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;
}
}
2. Create Test Case Class :-
- Create a java test class, say, TestJunit.java.
- Add a test method testPrintMessage() to your test class.
- Add an Annotaion @Test to method testPrintMessage().
- Implement the test condition and check the condition using assertEquals API of JUnit.
Create a java class file name TestJunit.java in C:\>JUNIT_WORKSPACE.
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());
}
}
3. Create Test Runner Class :-
- Create a TestRunner java class.
- Use runClasses method of JUnitCore class of JUnit to run the test case of the above created test class.
- Get the result of test cases run in Result Object.
- Get failure(s) using the getFailures() method of Result object.
- Get Success result using the wasSuccessful() method of Result object.
Create a java class file named TestRunner.java in C:\>JUNIT_WORKSPACE to execute test case(s).
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());
}
}
4. Compile the MessageUtil, Test case and Test Runner classes using javac.
C:\JUNIT_WORKSPACE>javac MessageUtil.java TestJunit.java TestRunner.java
5. Now run the Test Runner, which will run the test case defined in the provided Test Case class.
C:\JUNIT_WORKSPACE>java TestRunner
Verify the output.
Hello World
true
Now update TestJunit in C:\>JUNIT_WORKSPACE so that the test fails. Change the message string.
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.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 TestRunner
Verify the output.
Hello World
testPrintMessage(TestJunit): expected:<[New Word]> but was:<[Hello World]>
false