trigger Test_Share on Test__c (after insert) {

 if(trigger.isInsert){

 /**
 * Test_Share is the "Share" table that was created when the Organization Wide Default
*  sharing setting was set to "Private". Allocate storage for a list of Test_Share
* records.
 **/
 List<Test_Share> jobShares = new List<Test_Share>();

 /** For each of the Test records being inserted, do the following: **/
 for(Test__c t : trigger.new){

 /** Create a new Test_Share record to be inserted in to the Test_Share table. **/
 Test_Share studentRecord = new Test_Share();

 /** Populate the Test_Share record with the ID of the record to be shared. **/
 studentRecord.ParentId = t.Id;

 /** Then, set the ID of user or group being granted access. In this case,
 * we're setting the Id of the student__c that was specified by the Test
 * Result in the student__c lookup field on the Test record.
 **/

 studentRecord.UserOrGroupId = t.student__c;

 /** Specify that the Student should have edit access for this particular Test record. **/
 studentRecord.AccessLevel = 'edit';

 /** Specify that the reason the Student can edit the record is because its his test result
 * (Student_Access__c is the Apex Sharing Reason that we defined earlier.)
 **/
 studentRecord.RowCause = Schema.Test_Share.RowCause.Student_Access__c;

 /** Add the new Share record to the list of new Share records. **/
 jobShares.add(studentRecord);
 }

 /** Insert all of the newly created Share records and capture save result **/
 Database.SaveResult[] jobShareInsertResult = Database.insert(jobShares,false);
 }
}