Writing JUnit Tests

Question

Please, I am new to Java. How can I write a JUnit test for the program below:

Program to Test:

package codekeeper;

/**
 *
 * @author henryjoseph
 */
import java.util.*;
import java.io.*;

public class CodeKeeper {

    ArrayList<String> list;  //no specific amount..

    String[] codes = {"alpha","lambda","gamma","delta","zeta"};

    public CodeKeeper (String[] userCodes)
    {
        list = new ArrayList<String>();

        for(int i =0; i<codes.length;i++)
           addCode(codes[i]);

        for(int i =0; i<userCodes.length;i++)
            addCode(userCodes[i]);

        for(String code:list)
            System.out.println(code);
    }

    final void addCode(String code)
    {
        if(!list.contains(code))
            list.add(code);
    }

    public static void main(String[] args) {
        System.out.print("Enter your name and press Enter: ");
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String name = null;
        String[] argu = new String[] {name};
        try {
            name = br.readLine();

            argu = new String[] {name} ;
        }catch (IOException e) {
            System.out.println("Error!");
            System.exit(1);
        }
        CodeKeeper keeper = new CodeKeeper(argu);
    }
}

Sample Test Code:

public class MyClassTest {
    @Test
    public void testMultiply() {
        MyClass tester = new MyClass();
        assertEquals("Result", 50, tester.multiply(10, 5));
    }
}

Is this a standard way of writing the Junit Tests?

Answer 1

Usually one write code in a way it is testable, not vice versa.

Your code is not really testable since there is no method to query the state. When you add some methods to access the state, you could test a method which do change the state in test unit by checking the expected change.

Basically a test is

  @Test
  public void testConcept() {

      // 1. achieve a definite/initial state

      // 2. change this state by one or more methods under test

      // 3. assertXXX check expected changes

   }

In your current situation you could only test whether your code will throw an exception.

Answer 2

Some background first then some examples. When you write unit tests against your code you are testing a very specific and finite case of your application. What that means is that each unit test should cover at most one (1) scenario that a function (method) can receive. If you want to test multiple functions together you would be performing integration testing. Now if we take the following function that you have declared:

    final void addCode(String code)          
{   
           if(!list.contains(code))           
               list.add(code);           
} 

Assume that codeKeeper is properly initialized.
An appropriate unit test would look like this:

@Test(expected= NullPointerException.class)   
public void testAddCode_1() throws Exception  
{  
    codeKeeper.addCode(null);  
}  

Another appropriate usage is the following:

@Test()  
public void testAddCode_2() throws Exception  
{  
       codeKeeper.addCode("myMagicCode");
       assertTrue(codeKeeper.getList().contains("myMagicCode");  
}