2.3 Web interface

If you don't mind the inefficiency, you can use the website at http://submit.cs.usna.edu to manually upload all files for assignment submissions, then wait for the autotesting to complete and check the results.

Always double-check that you are submitting to the correct assignment name and that you submit all files for that assignment.

3 Testing your code

There are primarily two ways to test your Java code for this class. How you do the testing is totally up to you, but when we run your code we will usually be using JUnit.

3.1 Testing using main()

The simplest way to test your code is to make a main() method in some class, add commands to main that does whatever tests you want and prints the results to the screen, and then compile and run this program to check that your code is working.

This approach can work for simpler/smaller things, but it also has a few drawbacks:

• You have to check the output carefully to make sure everything is correct.
• It is hard to test every edge case and possibility without making the main method very long.
• For a large assignment, you may test something at the beginning, then forget to go back and test later to make sure you didn't accidentally break it.

3.2 Testing using JUnit4

JUnit4 is a standard and popular Java tool to automate repeated testing of your code in small, bite-sized pieces. It solves some of the drawbacks with main() method testing and is particularly useful for testing and debugging data structures.

Getting Junit4

First you have to download JUnit4. It should be installed on the lab machines already; on any other Ubuntu installation such as your VM or WSL, just run

sudo apt install junit4

Writing tests

Next, you need to write a class with test cases. Each test case is just a method in this class that has the @Test annotation. Within the test cases, you usually don't print things to the output. Instead, use the built-in assertions to check that things are as you expected.

For example, here is a complete JUnit test file with two test cases, which is checking the functionality of java.lang.String:

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

public class StringTest {
  @Test
  public void lengths() {
    String s1 = "something";
    assertEquals(9, s1.length());
    String s2 = "nothing";
    assertEquals(7, s2.length());
    assertFalse(s2.isEmpty());
  }

  @Test
  public void characters() {
    String s1 = "JUnit4";
    assertEquals('U', s1.charAt(1));
  }
}

There are many more useful features, including the ability to test that exceptions occur, and lots of other assertions. Check out the Junit4 wiki to learn more.

Compiling and running tests

To compile your test cases, you need to tell Java where to find the jar file for Junit4. The easiest way to do this is to set the CLASSPATH environment variable in bash:

export CLASSPATH=.:/usr/share/java/junit4.jar

Then, you can compile as usual with javac. To run your tests, you can do it like this, assuming your test cases are in a file called StringTest.java:

java -ea org.junit.runner.JUnitCore StringTest

Personally I find it annoying to type this every time, so I make a bash alias like so:

alias ju=(java -ea org.junit.runner.JUnitCore)

Then you can run tests just by typing (for example) ju StringTest

For even more convenience, edit your ~/.bashrc file and add the export CLASSPATH and alias ju commands shown above. Then whenever you start a new terminal those settings will already be applied.