TestCase #1:

1. Go to /jenkins/configure page
2. Set "# of executors" == any line, not a number
   Expected result: Validation error -  Not a number
   Actual result: No validation error
3. Click Apply
   Expected result: Validation error - Not a number. New configuration was not saved.
   Actual result: Error page:

   net.sf.json.JSONException: JSONObject["numExecutors"] is not a number.
   	at net.sf.json.JSONObject.getDouble(JSONObject.java:1948)
   	at net.sf.json.JSONObject.getInt(JSONObject.java:1967)
   	at jenkins.model.MasterBuildConfiguration.configure(MasterBuildConfiguration.java:54)
   	at jenkins.model.Jenkins.configureDescriptor(Jenkins.java:3715)
   	at jenkins.model.Jenkins.doConfigSubmit(Jenkins.java:3679)
           ..........
   

---------------------------------------------------

TestCase #2:

1. Go to /jenkins/configure page
2. Set "# of executors" == any negative number
   Expected result == Actual result: Validation error -  Not a number
3. Click Apply
   Expected result: Validation error - Not a number. New configuration was not saved.
   Actual result: New configuration saved.