Changed specification to rise an error when inserting with a negative index. Added new scenario to check this condition

spec/README.md

@@ -209,7 +209,7 @@ field must be a json scaped string.
     ]
     ```
 * **Sample Call**: `$ curl $KAPOW_URL/routes`
-* **Notes**: Currently all routes are returned; in the future, a filter may be 
+* **Notes**: Currently all routes are returned; in the future, a filter may be
   accepted.
 
 
@@ -314,10 +314,11 @@ A new id is created for the appended route so it can be referenced later.
     ```
 * **Notes**:
   * Route numbering starts at zero.
-  * When `index` is not provided or is less than `0` the route will be inserted
+  * When `index` is not provided or is `0` the route will be inserted
     first, effectively making it index `0`.
   * Conversely, when `index` is greater than the number of entries on the route
     table, it will be inserted last.
+  * Finally, when `index` is less than `0` a 422 error is raised.
   * A successful request will yield a response containing all the effective
     parameters that were applied.
 

spec/test/features/control/insert/error_unprocessable.feature

@@ -34,3 +34,21 @@ Feature: Kapow! server rejects insertion requests with semantic errors.
       """
     Then I get 422 as response code
       And I get "Invalid Route" as response reason phrase
+
+  Scenario: Error because negative index specified.
+    If a request contains a negative number in the
+    index field the server responds with an error.
+
+    Given I have a running Kapow! server
+    When I insert the route:
+      """
+      {
+        "method": "GET",
+        "url_pattern": "+123--",
+        "entrypoint": "/bin/sh -c",
+        "command": "ls -la / | response /body",
+        "index": -1
+      }
+      """
+    Then I get 422 as response code
+      And I get "Invalid Route" as response reason phrase