How to write test class for trigger...

trigger Update_Position on Candidate__c (before update, before insert) {

list<Id> Ids = new list<Id>();

list<Candidate__c> cIds = new list<Candidate__c>();

for(Candidate__c c : trigger.new) {

if(c.Position__c != null) {

Ids.add(c.Position__c);

cIds.add(c);  // The ids of keyword objects are here.

System.debug(‘Ids.size() is’+ Ids.size()+’cIDs is ‘+cIds[0].id);

}

}

list<Position__c> p =[select id, name from Position__c where id IN:Ids];

for(integer i=0;i<Ids.size();i++){

p[i].Candidate__c = cIds[i].id;

}

upsert(p);

}

==============================================================

@isTest

private class Update_Position_Test{

static testMethod void verify_Candidate() {

Position__c p = new Position__c();p.name = ‘Dummy position’;

p.Min_Pay__c=100;

p.Max_Pay__c=500;

upsert(p);

Candidate__c candidate = [select id, name from Candidate__c where name =:'Dummy Candidate'];

candidate.position__c = p.id;

system.debug(‘p.id is ‘ +p.id);

test.startTest();

upsert candidate; // The trigger gets called here.

test.stopTest();

Position__c positions = [select id,name, Candidate__c from position__c where name =: 'Dummy position'];

System.assertEquals(candidate.id,positions.Candidate__c);

}

}