Return the reason a username validation failed and add tests to verify we are sending the reason to client

test/test_api_usage.py

@@ -292,6 +292,24 @@ class TestCreateNewUser(ApiTestCase):
                                  expected_code=400)
 
     self.assertEquals('The username already exists', json['message'])
+
+  def test_trycreatetooshort(self):
+    json = self.postJsonResponse(User,
+                                 data=dict(username='a',
+                                           password='password',
+                                           email='test@example.com'),
+                                 expected_code=400)
+
+    self.assertEquals('Invalid username a: Username must be between 4 and 30 characters in length', json['error_description'])
+
+  def test_trycreateregexmismatch(self):
+    json = self.postJsonResponse(User,
+                                 data=dict(username='auserName',
+                                           password='password',
+                                           email='test@example.com'),
+                                 expected_code=400)
+
+    self.assertEquals('Invalid username auserName: Username must match expression [a-z0-9_]+', json['error_description'])
     
   def test_createuser(self):
     data = self.postResponse(User,