Validating Rules 
Your rules get validated for errors automatically. Additionally you can choose to run consistency checks for your rules.
Example
Create an If-Then rule and save it. You should see a warning saying the rule is incomplete and does not have conditions.
Create a complex expression, add an open bracket and save the changes. You should see an error message saying brackets do not match in complex expression.
Add condition values in a Decision Table that overlap such as between 15,000 and 20,000, between 17,000 and 25,000. You should see a warning message.
Add condition values in a Decision Table with a missing range such as between 15,000 and 20,000, between 25,000 and 40,000. You should see a warning message.
Note
An error message is a result of a validation check and cause problems when you execute the rules.
A warning message is a result of a consistency check and not necessarily cause any problem when you execute the rules.
Procedure
Your rules get validated, when you save changes in any editor or
in the Project Explorer view, in the context menu of a ruleset, flow ruleset or Project Resources node, you choose Validate.
To enable consistency checks:
In SAP NetWeaver Developer Studio, choose
Window 
Preferences 
.In the dialog box that appears, expand the Rules Composer node and choose Rule Validation.
In the screen that appears, select the checkbox:
Run rules consistency check
Choose OK.
NoteEnd of the note.
You should see warnings messages or error messages in the Problems view.
Double-click the message, to locate the relevant editor.
Note
If you do not see the Problems view:
In SAP NetWeaver Developer Studio, choose
Window Show View Other .In the dialog box that appears, expand the General node and choose Problems.
Choose OK.