diff --git a/adder.js b/adder.js
index 0c388fa..942df77 100644
--- a/adder.js
+++ b/adder.js
@@ -2,3 +2,7 @@ exports.add = function (x, y) {
 	return x + y;
 }
 
+exports.sub = function (x, y) { 
+	return x - y;
+}
+
diff --git a/test.js b/test.js
index 19f54c7..fd778cc 100644
--- a/test.js
+++ b/test.js
@@ -2,3 +2,6 @@ var adder = require('./adder'),
     assert = require('assert');
 
 assert(adder.add(4, 5) == 9);
+assert(adder.add(4, 6) == 10);
+assert(adder.sub(4, 5) == -1);
+