import org.junit.Assert;

import org.junit.Test;

import java.util.Arrays;

import java.util.Collections;

import java.util.HashSet;

import java.util.List;

public class PermutationsTest {

@Test

public void testPermute() {

Permutations p = new Permutations();

Assert.assertTrue(p.permute(new int[]{}).isEmpty());

List<List<Integer>> list0 = p.permute(new int[]{1});

Assert.assertTrue(list0.size() == 1);

Assert.assertEquals(new HashSet<>(list0),

new HashSet<>(Collections.singletonList(Collections.singletonList(1))));

List<List<Integer>> list1 = p.permute(new int[]{1, 2});

Assert.assertTrue(list1.size() == 2);

Assert.assertEquals(new HashSet<>(list1),

new HashSet<>(Arrays.asList(Arrays.asList(1, 2), Arrays.asList(2, 1))));

List<List<Integer>> list2 = p.permute(new int[]{1, 2, 3});

Assert.assertTrue(list2.size() == 6);

Assert.assertEquals(new HashSet<>(list2),

new HashSet<>(Arrays.asList(Arrays.asList(1, 2, 3), Arrays.asList(1, 3, 2), Arrays.asList(2, 1, 3), Arrays.asList(2, 3, 1), Arrays.asList(3, 1, 2), Arrays.asList(3, 2, 1))));

}

}