problem with JUnit test

Hi, i have class to generate random chars(a-f)
here is source:

Code:

---

package kodovac_rc1;



import java.util.ArrayList;
import java.util.Random;
 
    /**
    Třída slouží pro vygenerování neopakujících se hodnot a přepočítání do šestnáctkové soustavy
    */

public class randomGenerator {
   
    private static ArrayList<Integer> generate;
    private static final int INITIAL_SIZE = 16;
    private static String key = "";
 
    /**
    Metoda pro předávání hodnoty private proměnné jiné třídě
    */
    public static String vratKlic()
    {
        return key;
    }
   
    /**
    Metoda pro vytvoření generátoru
    */
    public static void randomGenerator() {
        generate = new ArrayList<Integer>(INITIAL_SIZE);
        fillList();
    }
   
    /**
    Metoda pro naplnění array čísli 10-16
    */   
    private static void fillList() {
        for (int i=10; i<INITIAL_SIZE; i++)
            generate.add(i);
    }
 
    /**
    Metoda pro vybrání čísla a převod do šestnáctkové soustavy
    */         
    public static void printRandomInt() {
        randomGenerator();
        Random pseudoNumber = new Random();
        int getThisElement;
        key = "";
       
        for (int i=10; i<INITIAL_SIZE; i++) {
            getThisElement = pseudoNumber.nextInt(generate.size());
            String c =Integer.toString(generate.remove(getThisElement), 16);
            key = key + c;
        }
    if(key.length()!=6)
    {
    printRandomInt();
    }
    }
}

---

This class worl for 100% i think...but test pass it only in 50% of cases...
here is test source:

Code:

---

/*
Testy třídy randomGenerator
 */
package kodovac_rc1;

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

/**
 *
 * @author Radek Mikulka
 */
public class randomGeneratorTest {
   
    public randomGeneratorTest() {
    }

    @BeforeClass
    public static void setUpClass() throws Exception {
    }

    @AfterClass
    public static void tearDownClass() throws Exception {
    }

    /**
    * Test metody vratKlic třídy randomGenerator.
    */
    @Test
    public void testVratKlic() {
        System.out.println("vratKlic");
        String expResult = "[a-f][a-f][a-f][a-f][a-f][a-f]";
        String result = randomGenerator.vratKlic();
        if(result.matches(expResult))
        {
        System.out.print("pass");   
        }else
        fail("Výstup neodpovídá regulárnímu výrazu. Někdy test neprojde i když metoda funguje na 100% správně.");
    }

    /**
    * Test metody testPrintRandomInt třídy randomGenerator.
    */
    @Test
    public void testPrintRandomInt() {
        System.out.println("printRandomInt");
        randomGenerator instance = new randomGenerator();
        randomGenerator.printRandomInt();
        System.out.println("Metoda musí proběhnout");
    }
}

---

WHY????

What does the testing software require? What are the 50% of cases that the code fails?

Which test fails, and why?

What are the possible values of this?

getThisElement = pseudoNumber.nextInt(generate.size());

Output is string with lenght = 6. Is created by 6 random nonrecurring chars connected together to one string. posslible values can be for example : abcdef, bfdace,efbcad,....... My problem is, that Test public void testVratKlic() fail sometime. For example: when I start tests, then testVratKlic() pass, i try it next time and void pass again, but when i try it several times the test will fail some times... Test is testing only if output of class matches to reguar expression. Thats why Iam afraid that my class does not work correctly. Sorry for my bad eng.

Would it help if you actually printed out the value of "result" on a failure?
Then you might actually see what it is that's being failed...at the moment you;re simply guessing.

problem is, that result is string.matech([a-f][a-f][a-f][a-f][a-f][a-f]) most of time...but sometimes imput value for test is empy...I dont know why :(((

getThisElement = pseudoNumber.nextInt(generate.size());

is selecting numbers from 0 to hex F, not A to F

Quote:

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Originally Posted by 2by4

getThisElement = pseudoNumber.nextInt(generate.size());

is selecting numbers from 0 to hex F, not A to F

---

Y but "generate" contins only numbers 10-15 and it is a-f in hex

Quote:

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Originally Posted by exltus

Y but "generate" contins only numbers 10-15 and it is a-f in hex

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ok I see. I agree with Tolls. Why not print out result?

Quote:

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Originally Posted by 2by4

ok I see. I agree with Tolls. Why not print out result?

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This is problem...I dont know why...And i dont see any error :(

Quote:

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I dont know why

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That is often the way it is until you find out why.
Printing out details as the code executes will often show you what is happening.

I think it may be because you are using static methods to initialize your data.

Is JUnit reloading your class between each test? What is the garbage collector doing???

Have you tried calling randomGenerator() in your test, just before you call vratKlic()?