What you think about having additional parameterized constru

Question

What you think about having additional parameterized constructor that would be used to pass in mock objects for unit testing only Would you consider it a bad design since test only code is being inserted to production code I m working on a very small project and do not want to add the complexity of a dependency injection framework and thinking about injecting mocks into the class this way only when doing unit testing Wondering if people find this as a bad design Another way would be ` VisibleForTesting` annotation to assign mocks to variables directly but I find injecting mocks via the constructor is easier to read and clarify which objects needs to be mocked

snowe · Answer

what do you mean pass in mock objects for unit testing only generally when you are mocking things you only mock what is passed into the constructor in the first place why would you need to add a separate parameterized constructor

Alan Lee · Answer

Well I create an instance of classes that I need in the class itself and do not need to have it passed in I want to replace this with mock objects during testing

snowe · Answer

can you post a code example

Alan Lee · Answer

``` class OtherClass var s String class BeingTested lateinit var otherClass OtherClass init if otherClass isInitialized otherClass = OtherClass normal constructor constructor other OtherClass this otherClass = other var normal = BeingTested var mocked = BeingTested other = OtherClass mocked print normal otherClass s print mocked otherClass s ```

Alan Lee · Answer

Here is a sample

Alan Lee · Answer

normal would print normal and mocked would print mocked

snowe · Answer

why does your class not take it in the original constructor

Alan Lee · Answer

I can change it so it could do that assigning a default value OtherClass does not need to be passed in I just want to change it to a mock when testing

Alan Lee · Answer

``` class OtherClass var s String class BeingTested var otherClass OtherClass = OtherClass normal var normal = BeingTested var mocked = BeingTested otherClass = OtherClass mocked print normal otherClass s print mocked otherClass s ```

Alan Lee · Answer

Here is a simplified example that uses a default parameter The point of my question is since I only use it to pass in a mock object would you consider this a bad design

Alan Lee · Answer

BTW Thanks for taking the time to look at this

snowe · Answer

I think that if you are using an internal class like that and you need to mock it then something else is designed wrong Here are the questions I would be asking myself modifying production code to make it testable indicates a code smell to me

snowe · Answer

1 Do you need this internal class

snowe · Answer

2 Why do you need it

snowe · Answer

3 Why can t it be passed in

snowe · Answer

4 Can a setter be used instead of an overridden constructor

Alan Lee · Answer

1 yes 2 It is required to implement feature for the given class 3 the external class or code does not know or doesn t need to know about the OtherClass

Alan Lee · Answer

4 Setter is also possible but again same question applies as it will be just used for testing

snowe · Answer

if external classes don t need to know about it then why do you need a mock

snowe · Answer

it seems there s a bit of an XY problem going on here maybe if you describe the actual problem I can better help

Alan Lee · Answer

Unfortunately I cannot share the actual code So there are some dependency and since the OtherClass is not what I want to test and also it is bit problematic to run Let s just say it does some network requests so would not want to run it in a unit test

snowe · Answer

sounds fine it seems like you should be passing it in as a parameter though not just for testing but always That way you can switch it out if you want

snowe · Answer

You don t need to write use a DI framework for it though

snowe · Answer

just pass it in in all the places you use it

Alan Lee · Answer

Thanks I could take various approaches to this but just wanted a quick opinion on the above approach from a good design perspective

snowe · Answer

You can also just use the Simple Factory pattern Create a wrapper class that instantiates your above class and passes in the proper OtherClass

snowe · Answer

Alan Lee · Answer

+1 Thanks for the link

snowe · Answer

np