I have a controller extension for a custom create child object page to take me back to the correct page after editing and to allow me to have an erorr message wthout using a validation. The controller works exactly as it should but I am having issues writing the test class for it. Iget the error "system.queryexception: list has no rows for assignment to sobject" My code is as below:
Controller:

public with sharing class createController {
	public String oppId {get;set;}
	public Opportunity opp;
	public Opportunity_Forecast__c oppf {get;set;}
	private ApexPages.StandardController stdController; 
	
    public createController(ApexPages.StandardController stdController) {
    	this.stdController = stdController;
        oppf = (Opportunity_Forecast__c)stdController.getRecord();
        String oppid = (oppf.Opportunity__c);
        String ID = ApexPages.currentPage().getParameters().get('oppid');
        opp = [select Automatic_Forecasting__c from Opportunity where Id =:ID]; 
        if (ID != null){
        	oppf.Opportunity__c= ID;   
        }   
    }
	
	public PageReference cancelAndReturn() 
    {
    	PageReference cancel = new PageReference('/' + ApexPages.currentPage().getParameters().get('oppid'));
        cancel.setRedirect(true);
 		return cancel;	
    }
	
	public PageReference saveAndReturn()
    {
        try{
        	if(opp.Automatic_Forecasting__c == true){
        		ApexPages.Message myMsg = new ApexPages.Message(ApexPages.Severity.ERROR,'Error: Upside Automation must be disabled on the opportunity page before editing forecasts.');
        		ApexPages.addMessage(myMsg);
        		return null;
        	}
        	else{
        		upsert oppf;
        		PageReference save = new PageReference('/' + ApexPages.currentPage().getParameters().get('oppid'));
        		stdController.save();
        		save.setRedirect(true);
        		return save;
        	}
        }
        catch(DMLException ex){
        	ApexPages.addMessages(ex);
        	return null;
        }
    }   
}

Test Class:

@isTest 
public with sharing class CreateControllerTest {
    static testMethod void testCreateController(){
    	
    	Account testAcct = new Account(Name='Test Create Controller');
    	insert testAcct;
    	
    	Opportunity opp = new Opportunity(Name = 'Test Opportunity1',Account = testAcct,Project_Start_Date__c = Date.newInstance(2017, 12, 15),Delivery_End_Date__c = Date.newInstance(2018, 9, 15),Forecast_Amount__c = 50000, StageName = 'Continued Development of Project',Opportunity_Region__c = 'UK',CloseDate = Date.newInstance(2011, 12, 15), Is_Test__c =TRUE, Automatic_Forecasting__c = FALSE, Test_Date__c = Date.newInstance(2017, 12, 18));
    	insert opp;
    	
    	Opportunity_Forecast__c oppf = new Opportunity_Forecast__c(Opportunity__c = opp.id, Value__c = 2000, Forecast_Category__c = 'Upside', Forecast_Period__c = 'Next Quarter');
    	insert oppf;
    	
    	Test.StartTest();
    	
    	PageReference pageRef = Page.NewForecast;
		Test.setCurrentPage(pageRef);
		pageRef.getParameters().put('id',oppf.Id);
    	ApexPages.StandardController sc = new ApexPages.StandardController(oppf);
        CreateController testOppForecast = new CreateController(sc);
 
        testOppForecast.saveAndReturn();
        Test.StopTest();
    }
}

Any ideas what I'm doing wrong? I've done some reading on the error I'm getting but most cases are where the record hasn't been created.