Java单元测试

Question

I have a program and I am trying to write my Unit Test for it, I just need to know if it is correct? Here is the program:

public static int[] bucketSort(int[] entries)
    {
        int numberBuckets = maxVal(entries);
        //Creates an array with maxVal buckets. 
        int[] buckets = new int[numberBuckets+1];
        //Loop through input entries and add one to the count for every occurrence of that number in entries.
        for (int i = 0; i < entries.length; i++)
        {
            buckets[entries[i]]++; 
        }
           int key = 0;
           for (int i = 0; i < buckets.length; i++)
           {
            for (int j = 0; j < buckets[i]; j++)
            {
                //Use the number of every occurrence of each number in entries to construct the sorted array.
                entries[key] = i;
                key++;
            }
           } 
           //Print out the sorted array.
            for(int i = 0; i <= entries.length-1; i++)
            {
                System.out.print(entries[i] + ", ");
            }
           return entries;
    }

Here is what I have for the Unit Test

import junit.framework.Assert;
import junit.framework.TestCase;

        public void testBucketSort()
        {
            int[] a1 = {9, 6, 2, 2, 4, 1, 0, 10,};
            int[] a2 = BucketSort.bucketSort(a);
            int[] a3 = {0, 1, 2, 2, 4, 6, 9, 10,};
            Assert.assertArrayEquals(a2, a3);
        }
    }

Answer 1

No this is not correct. There are two reasons:

You have used already sorted data. Though it should also be a test case, but you should use a random data set and apply sort on it. Keep another array like a3 as your expected array and then call assertArrayEquals on a2 and a3.

Your assertArrayEquals implementation is not verifying anything. Basically its just printing true or false but your test as such will always pass. You can use junit assertArrayEquals method from Assert class or right your own implementation where you should fail test if condition doesn't match.

Answer 2

Use JUnit, not your own testing method, unless you have a really good reason.

Also, think of how your code could break and write a test for each case. example:

1. all in order
2. reverse order
3. random order
4. all duplicate values

Make sure in all cases the result is exactly the right length and sorted appropriately.

Answer 3

The biggest problem that I see is that you're passing parameters to assertArrayEquals() in the wrong order: all JUnit assertions take parameters in the order expected , actual .

Other than that, you don't have nearly enough tests. For any array-based method, I would writeat least 4 tests: one with 0 elements, one with 1, one with 2, and one with 3. This will catch most edge cases (0, 1, 2), and give at least some assurance that your code will handle increasing sizes gracefully (3).