Luis Gómez Caballero Software Development

JUnit is a framework used to created tests in Java projects.

Installation

If we have Eclipse, it is not necessary to install it, because it is included. If we are not using an IDE, we have to download from its Web page (https://github.com/junit-team/junit4/wiki/Download-and-Install).

Creation of a new project

In Eclipse, we go to New Project / Java Proyect. We give a new name to the new project, and in the “Java Settings” screen, we have to inform that we are going to use the JUnit testing library. We click on the “Libraries” tab and on “Add Library…”. We select “JUnit” and “JUnit 4” version.

Java classes generation

First we need code to launch tests on it, so we create a small class with one method that returns a text string.

MyObject.java

package app;

public class MyObject {
	public String myMethod() {
		return "myString";
	}
}

JUnit test class generation

Now, we create a new class, but this time is not a “Class” type, but a “JUnit Test Case”.

Test method annotations

JUnit 4 brings several annotations to mark the methods that will be executed when launching the test (they will be used to lauch code before or after the tests or in first or last place when the test object gets instancied), but here we will only use @Test, that is used to mark methods as JUnit4 tests.

Test creation

In this test class, we create a method (with an autoexplicative name) and we use the instruction “assertEquals” to compare what it returns against what we expect it returns.

There are a lot of Assert types. Among them we can find “assertNotNull” or “AssertTrue”, that respectively compare that the tested object is not null and that it is True.

MyObjectTest

package app;

import static org.junit.Assert.*;

import org.junit.Test;

public class MyObjectTest {

	@Test
	public void testMyMethod() {

		MyObject myObject = new MyObject();

		assertEquals(myObject.myMethod(), "myString");
	}

}

Test execution

In order to execute a class with tests, we right-click on the name of the class in the Project explorer, and we click on “Run As…/JUnit test”.

We will see the JUnit with the test result and a green bar if successful, or red if failure.

Repository

The code of this demonstration can be located at https://github.com/luisgomezcaballero/junit4-demo.

Luis Gómez Caballero