JUnit: test builder with private field

Question

I'm a beginner and I have a problem with JUnit test in the constructor of a class.

The class that I want to test is called IntSortedArray and is as follows:

public class IntSortedArray {

    private int[] elements; 
    private int size; 


    public IntSortedArray() {
        this.elements = new int[16];
        this.size = 0;
    }

    public IntSortedArray(int initialCapacity) throws IllegalArgumentException {
        if(initialCapacity < 0) {
            throw new IllegalArgumentException("Error - You can't create an array of negative length.");
        }
        else {
            elements = new int[initialCapacity];
            size = 0;
        }
    }

    public IntSortedArray(int[] a) {
        elements = new int[a.length + 16];
        for(int i = 0; i < a.length; i++)
            elements[i] = a[i];
        size = a.length;
        insertionSort(elements);
    }

    //other code...

}

With Eclipse I created a class for JUnit:

public class IntSortedArrayUnitTest {

    private IntSortedArray isa;

    @Test
    public void testConstructorArray16Elements() {
        isa = new IntSortedArray();
        int expected = 0;
        for(int i: isa.elements) **<-- ERROR**
         expected += 1;
        assertEquals(expected, 16);
    }

}

I started to write a test class with the intention to test all the methods of the class IntSortedArray, including constructors.

The first method testConstructorArray16Elements() wants to test the first builder. So I thought I would check if the creation of the array elements is done properly, so the for loop counts how long elements and make sure it along 16 (as required).

But Eclipse generates (rightly) a mistake because elements is private. How can I fix this error? I don't want to put the public field and if possible I would like to avoid creating a method public int[] getElements().

What do you recommend?

Another question: I can do two assert the same method? One to test the length of the array and the other to test that size is 0.

I hope not to have made big mistakes, this is the first time I use JUnit.

PS: how can I test the second constructor?

Thank you very much!

score 0 · Accepted Answer · answered Mar 20 '15 at 21:24

It looks like your class fields are declare as private but you trying to access then from outside the class. You need to provide the accessors methods in you class to make them visible:

private int[] elements;
private int size; 
public static final int MAX = 16;

public int[] getElements() { ... }
public int getSize() { return size; }

Then you will be able to write below code:

isa = new IntSortedArray();
int expected = 0;
for(int i: isa.getElements()) {
  expected += 1;
}
assertEquals(expected, IntSortedArray.MAX );

It looks like your constructor has created an array for 16 integers, but does not initialize it with any value. To do that you should have below code:

public IntSortedArray() {
    this.elements = new int[MAX];
    this.size = 0;
    for (int i=0 ; i < MAX ;i++) {
       elements[i] = i;
       size++;
    }
}

Be aware that if `getElements()` returns `elements` then the caller can use this method to return the internal representation of the data (which might not be expected from a getter method) — NamshubWriter, Mar 23 '15 at 03:32
Yes, returning reference to your array will allow the caller to alter its content. To prevent this you should use already established technics, but this is out of the topic. That is why I did not provide code for it, You can read more about it [here](http://stackoverflow.com/a/12157504/4454454) — MaxZoom, Mar 23 '15 at 15:22

score -1 · Answer 2 · answered Mar 20 '15 at 21:14

-1

You'll have to write a getter method for your array, or implement an Iterator

answered Mar 20 '15 at 21:14

slux83

686
9
20

You can access the field via reflection if you really don't want to create a getter method – slux83 Mar 20 '15 at 21:23

JUnit: test builder with private field

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