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Discussion on: Unit Testing is Overrated

tyrrrz profile image
Alexey Golub Author

Just out of curiosity:

Mock out 3rd party dependencies & trust (but verify) that they work as intended.

How do you both trust and verify?

Maybe it was simply a bug in some edge case that you didn't consider, and it exposes some sensitive information to an attacker? While it doesn't crash your application directly, it's definitely something that needs fixing... and since it's in an edge case that wasn't considered before, you wouldn't have seen it until a user found it.

But if you considered it when writing a unit test, couldn't you consider it when writing a high-level test? Or conversely, if you didn't consider it when writing high-level test, you could very well also not consider it when writing unit tests.

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190245 profile image
Dave

How do you both trust and verify?

I saw your location & presumed you'd be familiar with the concept (a friend of mine moved from Kyiv to UK, it was him that I first heard the saying from). :)

In our case, at the unit test level, we simply trust that 3rd party dependencies function as their authors intend. There is a small review process that we go through before deciding to include a 3rd party dependency. Basically - if Apache Commons, go ahead, if it's some obscure Docker image on Docker Hub (non-certified) and only 4 other people have downloaded it... err... let's not touch that until it's more popular.

Then, at the integration test level (still in development), tests can be written to use the transport mechanism, or the file system etc (verifying that, for example, Commons IO or Gson dependencies actually do what we expect).

Later still, QA have tests (automated) that will inspect the model being transmitted across the "wire" etc - and they will flag up if we're exposing internal identifiers etc that another service (or the general public) don't explicitly need (all specified as part of the service design).

But if you considered it when writing a unit test, couldn't you consider it when writing a high-level test? Or conversely, if you didn't consider it when writing high-level test, you could very well also not consider it when writing unit tests.

Exactly.

I think my take there, is that it depends where you will fix the bug (with the benefit of hindsight), as to where you should be testing for it. If the bug is a simple "change this unit of code to fix it" then a unit test should be catching it (and this is one of the few use cases where TDD makes sense to me - I know the bug is in this code, so I'll write a test for it first, make the build fail, and then fix it).

However, if the bug is more subtle, and means that two (or more) units are working in unison to produce the problem further up (eg, A and B must be true, and both are in different units of code), then I'd write an integration test, and probably fix the issue(s) in the discrete unit(s). Then spend some time worrying about side effects & how we can potentially mitigate them.

My point being, unit tests are a necessary evil... but so are integration tests, QA tests (including manual testing) and in the majority of our cases, UAT too!

I agree that some companies/books/public speakers overly promote unit tests, but we certainly shouldn't be ignoring them entirely.

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tyrrrz profile image
Alexey Golub Author

Makes sense, thanks.

I was actually familiar with the concept but was curious what exactly you meant by it ;)

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boyen86 profile image
Boyen86

"I personally don't agree with this, especially that you should "always depend on an abstraction instead of an implementation". If your use case doesn't envision polymorphism and your abstraction is there "just in case", you've essentially wasted effort. There's nothing wrong with coupling if that's intentional, not all coupling should be avoided just because you can. In fact, most of your interfaces are still coupled to implementations in ways you may not realize until you try to introduce a second implementation."

I'd say your design process is just completely different than mine. When you are designing a class, you don't care about the implementation that you are communicating with. You don't create an interface because you want to introduce polymorphism, you create the interface because all you care about is "what" needs to happen, not "how" it needs to happen. Splitting what from how is absolutely essential when you want to create SOLID software. When you have proper separation of concerns, and your classes are single responsibility all you should care about is this interface, and thus, at that point in time, all you are writing is an interface.

What you propose is backwards you already have an implementation and then create an interface to start mocking. Honestly, it's not surprising why you dislike these tools for software design when you are following this path.

"What do you mean by low level bugs? Again, I would argue that if the bug never surfaces to the top level, it was never a bug to begin with."

High level tests do not test low level intricacies of a class. It can be something as simple as multiple enumerations because you forgot to do a .ToList() (or whatever) on a database query, causing you to perform the same query over and over again. Good luck finding that out on a high level integration test. You need to ensure in your design that what you have designed is actually doing what you expect it to do.

While you are writing this high level tests and you do want to go over all these low level intricacies you are holding a model of many classes (units) in your head. We write small units because complexity increases when the unit size increases. As such, the complexity of a test increases when you are increasing the scope of the test. So you are either

  1. Only testing the user functionality
  2. Writing really complicated tests to check all edge cases and functionalities of all lower level units

Or you just write your unit test while you are designing your software.

"From a high-level perspective, if your software works correctly according to the functional requirements, there might be a million bugs in your code that ultimately don't matter because they never surface in any way that would impact user experience. Instead, by not relying on internal specifics, you get the freedom to change and refactor your code however you want, as long as it doesn't invalidate the top-level public contract."

This is already an advantage of following SOLID standards, writing small units with a single purpose, that is easily exchangeable and reusable. Also, since you were programming against an interface to start with, the implementations don't matter.

Can I also mention that a million bugs in your software that "supposedly" don't surface because your integrations tests don't cover it can cost your organization a serious amount of money. I've been working in banking and offshore before my current job, downtime of half a day can easily cost you 100k, just because a developer didn't want to design the software properly.

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190245 profile image
Dave

Splitting what from how is absolutely essential when you want to create SOLID software. When you have proper separation of concerns, and your classes are single responsibility all you should care about is this interface, and thus, at that point in time, all you are writing is an interface.

In a perfect world, you're right. My employer certainly doesn't exist in a perfect world though.

What you propose is backwards you already have an implementation and then create an interface to start mocking.

I presume you're a TDD advocate. I mostly write the implementation first then test it, but I wouldn't be creating an interface just to add mocks in tests. I also wouldn't be creating an interface if I only have one concrete implementation - since that implementation effectively works as the interface, until I need to abstract it in some way.

High level tests do not test low level intricacies of a class.

This is a rather large overstatement. Don't they? Why not? Is it impossible to write a high level test that invokes the low level intricacies? Do all of those low level intricacies need to be tested? I'm currently conducting interviews, and rejected one candidate in part because they were writing tests for getters/setters.

downtime of half a day can easily cost you 100k

That's pretty cheap based on the industries I've worked in. In some regulated markets, the fine issued by the government authority for simply having to failover to the DR datacentre exceeds 100k, let alone other ancillary costs like loss of income.

End of the day, there has to be a balance. I personally think the title of this article was a little click-biased, and the author was trying to simulate a discussion by portraying a pretty biased argument. Nothing wrong with that, but the way I read it, the author doesn't entirely believe everything that they've written (as evidenced by my comment discussion with them).

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boyen86 profile image
Boyen86

"In a perfect world, you're right. My employer certainly doesn't exist in a perfect world though."

I'm not sure how this is relevant? We are just discussing how we are creating software. It's not as if it takes longer to create/maintain.

"I presume you're a TDD advocate. I mostly write the implementation first then test it, but I wouldn't be creating an interface just to add mocks in tests. I also wouldn't be creating an interface if I only have one concrete implementation - since that implementation effectively works as the interface, until I need to abstract it in some way."

I'm just wondering how the design process works. When you are writing class A and B, and A relies on B, but B is not yet written and you start with writing A, surely you'll program against the interface of B instead of its actual implementation? Anyway, that's how I do it. I will have an interface before an implementation 99.9999% of the time. I do not feel like a well defined interface is clogging up the code, for everyone that's not interested in the implementation it is an easy overview of the API.

And... even though I'd say it is irrelevant I'm neither an opponent nor advocate of TDD. In what order you write your tests or classes is for me an implementation detail. The interface here, however, is that your tests have a purpose in the design and maintenance of your code and that part is important.

"This is a rather large overstatement. Don't they? Why not? Is it impossible to write a high level test that invokes the low level intricacies? Do all of those low level intricacies need to be tested? I'm currently conducting interviews, and rejected one candidate in part because they were writing tests for getters/setters."

I do believe I gave some options in my post, and why you shouldn't be testing logic of low level classes on a high level (something with complexity)

Your tests should be SOLID just like your code base. As soon as you need to go over multiple aspects you are increasing the complexity of your code (test) and with that the readability. Just keep it simple is all that I'm advocating here.

You write tests for logic, if your getters and setters have logic... for whatever reason, I would surely want to test my logic while designing my class. If you are testing the framework of getters and setters I agree with you, but that honestly has nothing to do with with the intricacies (=logic) of the class that I am referring to.

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190245 profile image
Dave

We are just discussing how we are creating software. It's not as if it takes longer to create/maintain.

We're deliberately staying away from languages, and maybe it's just my approach, but rigidly sticking to SOLID principles (or any principles for that matter) certainly does take longer than me writing code and then tidying it up to obey principles whenever that's needed.

Don't get me wrong, I follow SOLID closely, right out of the gate, but just not strictly.

When you are writing class A and B, and A relies on B, but B is not yet written and you start with writing A, surely you'll program against the interface of B instead of its actual implementation?

That approach is counter-intuitive, at least to me. If A depends on B, but B is not written yet... I'd be starting with writing B. Only in the case that B is being written by someone else on the team would we agree an interface up front so both can work independently.

Just keep it simple is all that I'm advocating here.

I'm much the same, hence why I originally posted here that I think I'm somewhere between you & the original author.

You write tests for logic, if your getters and setters have logic...

In that case, I'd submit that they aren't getters and setters, and have side-effects that violate SOLID principles.

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boyen86 profile image
Boyen86

"In that case, I'd submit that they aren't getters and setters, and have side-effects that violate SOLID principles."

Hence my ".... for whatever reason", there's more to logic than side effects. For example, a myriad of if statements or whatever. All things that don't belong in a getter or setter, but if you insist that it should be in the getter or setter, at least write a contract (=test) on how you intend the getter or setter should behave.

And that's the core of this whole discussion right? Is it necessary to test logic that isn't directly visible to the outside world?

You could say, if it isn't directly visible then it doesn't need to be tested. I'd say if the code is there, it is there for a reason, if it there for a reason it should be tested. If the code is not there for a reason, get rid of it. And all these questions would've been circumvented if your tests were written during the design of a class.

You can potentially test this in a big integration test, but, why would you? I'd say that's a violation of KISS principles because the coupling between a class and its contract is lost and I, as a developer working on your code need to jump through hoops just to find out how you intended your piece of software to work.

"We're deliberately staying away from languages, and maybe it's just my approach, but rigidly sticking to SOLID principles (or any principles for that matter) certainly does take longer than me writing code and then tidying it up to obey principles whenever that's needed."

Sure, perhaps, I don't think I'm necessarily faster than a two-step approach. And everything perfect in one go is utopic, sometimes it takes refactoring to get things right.

I do feel like it is our responsibility as software engineers to either convince our employer that a standardized approach is beneficial, and also that as an expert in the field, it is good to say no. I hope that writing standardized software doesn't only occur in a perfect world.

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190245 profile image
Dave

I do feel like it is our responsibility as software engineers to either convince our employer that a standardized approach is beneficial, and also that as an expert in the field, it is good to say no.

On this, we both agree. I also know that I've been in situations in the past where arguing for standardisation has fallen on deaf ears.

There's a multitude of reasons why others in the business will try to get us to cut corners, to deliver slightly faster etc. Sometimes we can say no, sometimes we're overruled.

Hence my belief that 100% standardised code, does indeed only exist in a perfect world. Maybe 80% or so is a more realistic aim.