import org.drools.test.RuleTester.Foo;

rule "notNotRule"
    when        
        exists ( Foo() );        
    then     
        System.out.println("Rule fired...");      
end
import org.drools.test.RuleTester.Foo;

rule "existsRule"
    when        
        exists ( Foo() );        
    then     
        System.out.println("exists rule fired...");      
end