Test class for VF page that displays attachments from related record

Hi there,

I have created a VF page to display an image attachment from a Contact on a custom object. The VF page and controller are working, but I am having trouble with the test class for it. The problem I am having is that I am not sure how to reference the current record in the test. 

Controller:

Public Class displayImageExtension {
    public Fund_Relationships__c currentRecord {get; set;} 
    public displayImageExtension(ApexPages.StandardController controller) {
        currentRecord = [SELECT Id, Contact__c FROM 
                         Fund_Relationships__c WHERE Id = :ApexPages.currentPage().getParameters().get('id')];    
    }
    public String getFileId() {
        String fileId = '';
        List<Attachment> attachedFiles = [select Id FROM Attachment WHERE parentId =:currentRecord.Contact__c AND Name LIKE '%Sig%' order By LastModifiedDate DESC limit 1];
        if (attachedFiles.size() == 0){
            ApexPages.addmessage(new ApexPages.message(ApexPages.severity.INFO,'No signature image found'));
            return null;
      } 
        if( attachedFiles != null && attachedFiles.size() > 0 ) {
            fileId = attachedFiles[0].Id;
        }
        return fileId;    
    }
}

VF Page

<apex:page standardController="Fund_Relationships__c" extensions="displayImageExtension">
<apex:form >
    <apex:image url="/servlet/servlet.FileDownload?file={!FileId}" width="300" rendered="{!IF(FileId !="",True,False)}"/>
<apex:pageMessages id="showmsg"></apex:pageMessages>
</apex:form>
</apex:page>

Test Class (23% coverage)

@isTest
private class TestdisplayImageExtension {
    static testMethod void MyTest(){
        Account myaccount = new Account (name='Test');
		insert myaccount;
        Contact mycontact = new Contact (firstname='Billy', lastname='Baggins');
        insert mycontact;
        Attachment attach = new Attachment();
  		attach.Name = 'Signature_File';
  		Blob bodyBlob = Blob.valueOf('Testing Body of Attachment');
  		attach.body = bodyBlob;
  		attach.parentId = mycontact.id;
  		insert attach;
        Fund__c myfund = new Fund__c();
        myfund.Name = 'Test Fund';
        myfund.Account__c = myaccount.id;
        myfund.Entity__c = 'SIF';
        myfund.Fund_Type__c = 'Social Enterprise Loan';
        myfund.Type__c = 'Term Loan';
        myfund.Status__c = 'New';
        myfund.Open_Date__c = date.today();
        insert myfund;
        Fund_Relationships__c fundauth = new Fund_Relationships__c();
        fundauth.Contact__c = mycontact.id;
        fundauth.Fund__c = myfund.id;
        fundauth.Role__c = 'General';
        fundauth.Role_Status__c = 'Current';
        fundauth.Start_Date__c = date.today();
        insert fundauth;
        displayImageExtension controller = new displayImageExtension(new ApexPages.StandardController(fundauth));
List < Attachment > attachedFiles = [select id, name from Attachment where parent.id = : mycontact.id];
 System.assertEquals(1, attachedFiles.size());
String newAttachId = controller.getFileId();
 System.assertEquals(newAttachId, attachedFiles[0].Id);
    }
}

Any help with this would be greatly appreciated!

-- Ken