sort/MergeSortTest.java

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package sort;

import static org.junit.Assert.*;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Random;

import org.junit.Test;

public class MergeSortTest {
    final static int seedVal = 127;

    private Random rand = null;
    private MergeSort<Integer> mSort = null;

    public MergeSortTest() {
        rand = new Random(seedVal);
        mSort = new MergeSort<Integer>();
    }

    private void initArray(ArrayList<Integer> a, final int N) {
        final int randRange = N * 2;
        for (int i = 0; i < N; i++) {
            a.add(rand.nextInt(randRange));
        }
    }

    private <T extends Comparable<T>> boolean isSortedArray(ArrayList<T> a) {
        boolean isSorted = true;
        for (int i = 0; i < a.size() - 1; i++) {
            // a[i] should be <= a[i+1] of if a[i] is > a[i+1] then the sort
            // failed
            if (a.get(i).compareTo(a.get(i + 1)) > 0) {
                isSorted = false;
                break;
            }
        }
        return isSorted;
    }

    private boolean testSort(int N) {
        boolean passed = true;

        if (N > 0) {
            ArrayList<Integer> vals = new ArrayList<Integer>();
            initArray(vals, N);
            mSort.mergeSort(vals);
            passed = isSortedArray(vals);
        } else {
            mSort.mergeSort(null);
        }
        return passed;
    }

    @Test
    public void testNullArray() {
        assertTrue("MergeSort test failed for null array", testSort(0));
    }

    @Test
    public void testEvenElement() {
        // test sorting an even number of values
        assertTrue("MergeSort test failed for even numbers of values",
                testSort(64));
    }

    @Test
    public void testOddElement() {
        assertTrue("MergeSort test failed for odd numbers of values",
                testSort(127));
    }

    @Test
    public void testOneElement() {
        // test for 1 value
        assertTrue("MergeSort test failed for 1 value", testSort(1));
    }

    @Test
    public void testTwoElements() {
        // test for 2 value
        assertTrue("MergeSort test failed for 2 values", testSort(2));
    }

    @Test
    public void testStringSort() {
        ArrayList<String> words = new ArrayList<String>(Arrays.asList("T'was",
                "brillig", "and", "Slithey", "Toves", "all", "mimsy", "were",
                "the", "borogroves", "and", "moonraths", "outgrabe"));
        MergeSort<String> strSort = new MergeSort<String>();
        strSort.mergeSort(words);
        boolean sorted = isSortedArray(words);
        assertTrue("MergeSort test failed for String sort", sorted);
    }
}