Test custom controller that does not use parameters directly

Question

Given a custom controller that uses a record selected by a standard controller (not through id parameter), how can I ensure that the appropriate Custom_Field__c field is available in the unit test?

On the page, I add the hidden input field so that Salesforce picks up the backing field:

<apex:inputHidden value="{!Custom_Object__c .Custom_Field__c }"/>

Then, in the controller, I rely on the existence of the field to verify if the record is ok:

public with sharing class CustomController {

    private Custom_Object__c obj;

    public CustomController (ApexPages.StandardController stdCtrl) {
        this.obj = (Custom_Object__c )stdCtrl.getRecord();

        // selected due to <apex:inputHidden value="{!Custom_Object__c .Custom_Field__c }"/>
        if (obj.Custom_Field__c == false) {
             throw new CustomException('Error message.');   
        }
    }
}

If I test with something like this:

    Test.setCurrentPage(new PageReference('/apex/CustomPage?id=' + obj.Id));

    ApexPages.StandardController stdCtrl = new ApexPages.StandardController(obj);
    CustomController ctrl = new CustomController (stdCtrl);

then a CustomException gets thrown because the field Custom_Field__c is not available to the controller.

I know that I could capture the ID through the parameter and then select the record

 Id recordId = ApexPages.currentPage().getParameters().get('id');
 this.obj = [select Id, Custom_Field__c from Custom_Object__c where Id = :recordId];

However, I'd like to keep the default record Id checking from Salesforce (so that one cannot manually input an Id of a record with a wrong object type). I'm also aware that this can be prevented with something like:

Id recordId = ApexPages.currentPage().getParameters().get('id');
if (recordId.getSObjectType() != Custom_Object__c.sObjectType) {
    throw new CustomException('Wrong object type.');    
}

Still, I'm interested in the original question.

Answer 1

When you are providing an object to the standard controller, you are responsible for selecting the appropriate record and its fields instead of the standard controller. In a test, that would look like this:

Custom_Object__c obj = [Select Custom_Field__c from Custom_Object__c where Id = :someId limit 1];
ApexPages.StandardController stdCtrl = new ApexPages.StandardController(obj);

or even:

Custom_Object__c obj = new Custom_Object__c(Custom_Field__c = true); // or = false
ApexPages.StandardController stdCtrl = new ApexPages.StandardController(obj);

(if the record doesn't need to be in the database). This standard controller can then be passed to a custom controller:

CustomController ctrl = new CustomController (stdCtrl);

So a workaround is to provide the correct record (with the required fields selected) yourself.