diff --git a/primitiveCollections/src/main/java/org/lucares/collections/IntList.java b/primitiveCollections/src/main/java/org/lucares/collections/IntList.java
index c1325d4..872c991 100644
--- a/primitiveCollections/src/main/java/org/lucares/collections/IntList.java
+++ b/primitiveCollections/src/main/java/org/lucares/collections/IntList.java
@@ -738,9 +738,8 @@ public final class IntList implements Serializable, Cloneable {
 	@Override
 	public String toString() {
 
-		if (data == null)
-			return "null";
-		final int iMax = data.length - 1;
+		assert data != null : "data cannot be null";
+		final int iMax = size - 1;
 		if (iMax == -1)
 			return "[]";
 
diff --git a/primitiveCollections/src/test/java/org/lucares/collections/IntListTest.java b/primitiveCollections/src/test/java/org/lucares/collections/IntListTest.java
index ed26ed4..f4b6413 100644
--- a/primitiveCollections/src/test/java/org/lucares/collections/IntListTest.java
+++ b/primitiveCollections/src/test/java/org/lucares/collections/IntListTest.java
@@ -521,9 +521,13 @@ public class IntListTest {
 		final IntList a = new IntList();
 		final IntList b = new IntList();
 
+		// on empty lists
+		Assert.assertTrue(a.equals(b));
+		Assert.assertEquals(a.hashCode(), b.hashCode());
+
+		// on equal lists
 		a.addAll(1, 2, 3, 4);
 		b.addAll(1, 2, 3, 4);
-
 		Assert.assertTrue(a.equals(b));
 		Assert.assertEquals(a.hashCode(), b.hashCode());
 
@@ -533,11 +537,27 @@ public class IntListTest {
 		Assert.assertTrue(a.equals(b));
 		Assert.assertEquals(a.hashCode(), b.hashCode());
 
+		// TODO sorted and unsorted lists with same length
+
 		// change one value
 		a.remove(2, 3);
 		a.insert(2, 99);
 		Assert.assertFalse(a.equals(b));
 		Assert.assertNotEquals(a.hashCode(), b.hashCode());
+
+		// have different length
+		a.add(66);
+		Assert.assertFalse(a.equals(b));
+		Assert.assertNotEquals(a.hashCode(), b.hashCode());
+
+		// same object
+		Assert.assertTrue(a.equals(a));
+
+		// other is null
+		Assert.assertFalse(a.equals(null));
+
+		// equals with a different class
+		Assert.assertFalse(a.equals("not an IntList"));
 	}
 
 	@Test