I am creating unit tests for a custom controller I created to handle file uploads and am having issues populating the Attachment body property in my test method. I really just don't know how I'm supposed to simulate a file upload during unit testing.

The body property is normally populated from the visualforce apex:inputFile tag, where I bind the inputFile to the attachment body property in my controller.

<apex:inputFile value="{!file.body}" />

I know that the Attachment body must be encoded in Base64, but how do I create a variable in my test class that I can use for filesize bounds testing as well? Can anyone provide some direction or even code samples on how I would go about doing this?

My test method is as follows:

static testMethod void basicControllerTest()
{
System.debug('Unit Test: AttachOppPaperwork Controller');

//Create Opportunity record
Opportunity o = new Opportunity();
o.name = 'Test Opp 1';
o.stageName = 'First Appointment';
o.closeDate = system.today()+60;
insert o;

//Set current page to AttachOppPaperwork
PageReference oPage = new PageReference('/apex/AttachOppPaperwork?id='+o.Id);
Test.setCurrentPage(oPage);

//Instantiate Controller
AttachOppPaperworkController c = new AttachOppPaperworkController();

//Verify variable values
System.assertEquals(o.name, c.oppName); //c.oppName == [Opportunity Name]
System.assertEquals(o.id, c.oppId); //c.oppId == [Opportunity Id]
System.assertNotEquals(null, c.file); //c.file instantiated

//Test File Upload
System.debug('-->AttachOppPaperworkController.upload() called');

//Set file body
//???

//upload the attachment
PageReference uploadTest = c.upload();

System.debug('::AttachOppPaperworkController.attachmentId = ' + c.attachmentId);
System.assertNotEquals(null, c.attachmentId); //attachmentId property should not be null
System.assertEquals(null, uploadTest); //method should return null, refreshing the page
System.assertEquals(true, c.complete); //complete flag should be set to true

//Verify Opportunity field update
Opportunity oTest = [SELECT PaperworkUploadedDate__c FROM Opportunity WHERE Id=:o.Id];

System.debug('::PaperworkUploadedDate__c = ' + oTest.PaperworkUploadedDate__c);
System.assertNotEquals(null, oTest.PaperworkUploadedDate__c); //date field should have a value
}