I've a trigger which runs 'before update' on opportunity. Now  trying to writing test class for that trigger. In testmethod, there are statements: 

 Opportunity getOpp = [select name, amount, contract__c from opportunity where id = '00690000005t1d1'];

getOpp.amount =  5000.00;

update getOpp;

but while running, getting following error on query line : 

System.QueryException: List has no rows for assignment to SObject.

I tried fixing left side to 'Opportunity[] getOpp' , but then , as I was expecting... error transmit to iind line ( in that case IInd line is getOpp[0].amount, gives error like .. 'out of bound' etc  ). This suggest query is not returning any thing ..

But point here is,  opportunity with mentioned ID does exist in system; while running the same query in system log console, it works fine!.. question is, why it is failing inside test method ? Do testmethods always need testdata, created inside test class ? 

IInd thing : to fix above ...  I also tried to create opportunity within test class

date mydate = date.parse('02/27/2012');
   Opportunity oppContract= new opportunity( name = 'just for testclass', closedate = mydate , stageName ='Qualification',
    contract__c = '80090000000Dp6R' );
    insert oppContract ;

( note :here contract__c is look up field to contract object)  

I then get "same" opportunity using soql query  and  try to update it

 But now  trigger which run on update start giving error .It   has statements like these :

  Map<id,contract> MapofCons = new Map<id,contract>([select id, name,sum_total__c from contract where id in :<setofIds>]);

for (opportunity o : trigger.new )

 If( MapofCons.get(o.contract__c).sum_total__c ==null) 

here I  get error  on " IF statement' , like this  :  System.NullPointerException: Attempt to de-reference a null object (on above line). which  shows , it is not able to reference  contract  object....

I'm little confused, how to proceed now ...please help ! 

Note : using developer edition for all this ....