diff --git a/test/index.js b/test/index.js
index 93cd315..3b2878c 100644
--- a/test/index.js
+++ b/test/index.js
@@ -72,3 +72,31 @@ test ('run non-global regex without result', (t) => {
   });
   t.is (count, 0);
 });
+
+test ('check isnil with undefined', (t) => {
+  t.is (util.is_nil (), true);
+});
+
+test ('check isnil with null', (t) => {
+  t.is (util.is_nil (null), true);
+});
+
+test ('check isnil with empty string', (t) => {
+  t.is (util.is_nil (''), false);
+});
+
+test ('check isnil with string', (t) => {
+  t.is (util.is_nil ('foo'), false);
+});
+
+test ('check isnil with 0', (t) => {
+  t.is (util.is_nil (0), false);
+});
+
+test ('check isnil with nan', (t) => {
+  t.is (util.is_nil (parseInt ('foo')), true);
+});
+
+test ('check isnil with int', (t) => {
+  t.is (util.is_nil (parseInt ('42')), false);
+});