Guide to Object-oriented Programming With Java (University at Buffalo Version)

Chapter 13: JUnit Testing and Using the Debug Tool

Testing an Application Using Junit

The eclipse IDE allows you to use Junit to create unit tests to test individual sections of yourr Java code.

A `DistanceConverter.java` Example

Before you can write any unit tests you need to create the application to be tested. For example, DistanceConverter.java

package edu.buffalostate.cis425.fa21.guide.your-last-name;

public class DistanceConverter {

public static double convertFeettoMeters(double feet) {
return feet * 0.3048;
}

public static double convertMeterstoFeet(double meters) {
return meters * 3.2808;
}

public static void main(String[] args) {
System.out.println("1 foot = " + convertFeettoMeters(1) + " meters\n");
}
}

Figure 13-1: DistanceConverter.java Code

Console — Figure 13-2: `DistanceConverter.java` Output

Creating the Junit Test Template

Use the following steps to create a template Junit test for your DistanceConverter.java file.

Right click on your DistanceConverter.java File
Choose: New -> Junit Test Case
In the Name: field, type: DistanceConverterTest.java
Click the Finish button
Note: The first time you use Junit you may need to click the link to setup the Junit 4 library in your project properties.
You should now see the template in the edtor window

Figure 13-3: Using java.io.util.Scanner to Read a File Code

package edu.buffalostate.cis425.fa21.guide.your-last-name;

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

public class DistanceConverterTestEmpty {
@Test
public void test() {
fail("Not yet implemented");
}
}

Figure 13-4: Using java.io.util.BufferedReader to Read a File Output

Adding Test Cases

Now you are ready to add some test cases to the DistanceConverterTest.java file:

package edu.buffalostate.cis425.fa21.guide.your-last-name;

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

public class DistanceConverterTestEmpty {

double feet, meters;

@Test
public void testConvertFeettoMeters() {
feet = 2;
meters = DistanceConverter.convertFeettoMeters(meters);
assertEquals(meters, 0.3048, 0.001);
}

@Test
public void testConvertMeterstoFeet() {
meters = 2;
meters = DistanceConverter.convertMeterstoFeet(feet);
assertEquals(3.281,feet, 0.001);
}
}

Figure 13-5: Adding Test Cases to DistanceConverterTest.java Code

Now run your DistanceConverterTest.java file to produce the following window.

Note: the above example has a test failure because the test case for convertFeettoMeters() is testing for feet to be a 2 but we assert (expects) it to be a 1.

Using the Eclipse Debug Tool

Eclipse has a built-in debug tool that provides a way to walk through your code and observe values for your variables and objects. You can set breakpoints so that when you run your code Eclipse will stop at the next breakpoint. This is a handly tool to determine if your variables have a value that you expect them to have and to help figure out why you may be getting unexpected results.