diff --git a/test.js b/test.js
index 5a51526..1968dad 100644
--- a/test.js
+++ b/test.js
@@ -85,6 +85,7 @@ exports.extend = {
 
 exports.filterable = {
   distributivity: test(x => filterable.distributivity(equality)(Id[fl.of]([0, 1, 2, 3, 4]))(x => x % 2 === 0)(x => x > 0)),
+  identity: test(x => filterable.identity(equality)(Id[fl.of]([1, 2, 3]))),
   annihilation: test(x => filterable.annihilation(equality)(Id[fl.of]([1, 2, 3]))(Id[fl.of]([4, 5, 6]))),
 };