Missing Return Statement When Implementing the StubProvider Interface

Question

I am trying to implement the StubProvider Interface as Kevin Poorman does in his blog here: Kevin's Month of Testing Blog - Part 3 of 3 and on line 3 I am getting the error 'Missing return statement required return type: Object.' What could I possibly be doing wrong? Also, because we are in between releases, yes, I am in a sandbox that is running Summer '18, so it isn't (or, shouldn't be) the switch statement causing this issue. Ideas?

@isTest
public class AttachmentTriggerDisabledMockStub implements System.StubProvider {
    public Object handleMethodCall(Object stubbedObject, String stubbedMethodName,
                                   Type returnType, List<Type> listOfParamTypes, 
                                   List<String> listOfParamNames,
                                   List<Object> listOfArgs){
        switch on stubbedMethodName{
            when 'Disable_Attachment_AD__c', 'Disable_Attachment_AI__c', 'Disable_Attachment_AU__c'{
                return false;
            }      
        }                                        
    }    
}

Answer 1

When a method has a non-void return type, you're responsible for ensuring that all code paths are terminated by a return statement.

In this case, your switch statement prescribes the return value for a specific set of logic paths, but the compiler can't guarantee that the condition will be true. You need to provide a return statement (it can be return null;) to ensure that a return value is provided should your condition not execute. This is true regardless of the logical construct being used (it's not unique to the switch construct).

To use a simple example, the following is not allowed, because the compiler cannot guarantee that a return value will be provided:

public static Object retVal(String input) {
    switch on input {
        when 'Test' {
            return true;
        }
    }
}

This is one way to make it legal, using when else to cover any case not already handled by a when block:

public static Object retVal(String input) {
    switch on input {
        when 'Test' {
            return true;
        }
        when else {
            return false;
        }
    }
}

That guarantees that there will be a return value, regardless of the logical path followed and regardless of the input parameter.

Another way to deal with the issue is to place a simple return statement after the switch. This applies equally to other logical constructs.

public static Object retVal(String input) {
    switch on input {
        when 'Test' {
            return true;
        }
    }

    return false;
}