add stream() and parallelStream()

Both methods return an IntStream.

primitiveCollections/src/test/java/org/lucares/collections/IntListTest.java

@@ -7,8 +7,10 @@ import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.util.Arrays;
 import java.util.List;
+import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.stream.Collectors;
+import java.util.stream.IntStream;
 
 import org.junit.Assert;
 import org.junit.Test;
@@ -474,4 +476,58 @@ public class IntListTest {
 		list.set(1, 0);
 		Assert.assertNotEquals(list, clone);
 	}
+
+	@Test
+	public void testToString() {
+		Assert.assertEquals("[]", new IntList().toString());
+
+		final IntList list = new IntList();
+		list.addAll(-2, -1, 0, 1, 2);
+		Assert.assertEquals("[-2, -1, 0, 1, 2]", list.toString());
+		Assert.assertEquals("same result as Arrays.toString()", Arrays.toString(list.toArray()), list.toString());
+	}
+
+	@Test
+	public void testSequentialStream() {
+
+		{
+			final IntList list = new IntList();
+			list.addAll(0, 1, 2, 3, 4, 5, 6);
+			final IntStream stream = list.stream();
+			Assert.assertEquals(list.size(), stream.count());
+		}
+		{
+			final IntList list = new IntList();
+			list.addAll(0, 1, 2, 3, 4, 5);
+			final IntStream stream = list.stream();
+			Assert.assertEquals(15, stream.sum());
+		}
+		{
+			final IntList emptyList = new IntList();
+			Assert.assertEquals(0, emptyList.stream().count());
+		}
+	}
+
+	@Test
+	public void testParallelStream() {
+		final IntList list = new IntList();
+
+		final int size = 1000;
+		final int[] ints = new int[size];
+		for (int i = 0; i < size; i++) {
+			ints[i] = i;
+		}
+
+		list.addAll(ints);
+
+		final ConcurrentLinkedQueue<Integer> processingOrder = new ConcurrentLinkedQueue<>();
+		final List<Integer> actualList = list.parallelStream()//
+				.peek(e -> processingOrder.add(e))//
+				.boxed()//
+				.collect(Collectors.toList());
+
+		Assert.assertEquals("should be sequential, when using collect", actualList.toString(), list.toString());
+		Assert.assertNotEquals("should use parallelism during computation", processingOrder.toString(),
+				list.toString());
+	}
 }