Improve error message when req argument missing

HISTORY.md

@@ -1,6 +1,7 @@
 unreleased
 ==========
 
+  * Improve error message when `req` argument missing
   * perf: enable strict mode
   * perf: hoist regular expression
   * perf: parse with regular expressions

index.js

@@ -46,6 +46,10 @@ var userPassRegExp = /^([^:]*):(.*)$/
  */
 
 function auth(req) {
+  if (!req) {
+    throw new TypeError('argument req is required')
+  }
+
   // get header
   var header = (req.req || req).headers.authorization
 

test/index.js

@@ -9,7 +9,15 @@ function request(authorization) {
   }
 }
 
-describe('auth(req)', function(){
+describe('auth(req)', function () {
+  describe('arguments', function () {
+    describe('req', function () {
+      it('should be required', function () {
+        assert.throws(auth, /argument req is required/)
+      })
+    })
+  })
+
   describe('with no Authorization field', function(){
     it('should return null', function(){
       var req = request();