school__c -->customObject
studentjoinage =system.today() - createddate; //its formula field which riturn number.
I written the batchclass,in that   if(sch.studentjoinage__c==30) then send an email.
test.starttest
   mybatchcls mb=new mybatchcls();
   database.execute();
test.stoptest;
i get 40% codecoverage, in that start method ,finish methods r coverd but in execute method after if condition which means
messaging.singleemailmessage not coverd bcoze formula field.
i need help here to cover formula field.