Unit, integration, subcutaneous, UI, fast, slow, mocks, TDD, isolation and scams… What is this? I don’t even!

As outlined in the first post of my Automated Testing blog series I’ve been on a journey of self reflection and discovery about how best to write, structure and maintain automated tests.

The most confusing and profound realisations that I’ve had relate to how best to cover a codebase in tests and what type and speed those tests should be. The sorts of questions and considerations that come to mind about this are:

  • Should I be writing unit, subcutaneous, integration, etc. tests to cover a particular piece of code?
  • What is a unit test anyway? Everyone seems to have a different definition!
  • How do I get feedback as fast as possible – reducing feedback loops is incredibly important.
  • How much time/effort are we prepared to spend testing our software and what level of coverage do we need in return?
  • How do I keep my tests maintainable and how do I reduce the number of tests that break when I need to make a change to the codebase?
  • How do I make sure that my tests give me the maximum confidence that when the code is shipped to production it will work?
  • When should I be mocking the database, filesystem etc.
  • How do I ensure that my application is tested consistently?

In order to answer these questions and more I’ve watched a range of videos and read a number of blog posts from prominent people, spent time experimenting and reflecting on the techniques via the projects I work on (both professionally and with my Open Source Software work) and tried to draw my own conclusions.

There are some notable videos that I’ve come across that, in particular, have helped me with my learning and realisations so I’ve created a series of posts around them (and might add to it over time if I find other posts). I’ve tried to summarise the main points I found interesting from the material as well as injecting my own thoughts and experience where relevant.

There is a great talk by Gary Bernhardt called Boundaries. For completeness, it is worth looking at in relation to the topics discussed in the above articles. I don’t have much to say about this yet (I’m still getting my head around where it fits in) apart from the fact that code that maps input(s) to output(s) without side effects are obviously very easy to test and I’ve found that where I have used immutable value objects in my domain model it has made testing easier.

Summary

I will summarise my current thoughts (this might change over time) by revisiting the questions I posed above:

  • Should I be writing unit, subcutaneous, integration, etc. tests to cover a particular piece of code?
    • Typical consultant answer: it depends. In general I’d say write the fastest possible test you can that gives you the minimum required confidence and bakes in the minimum amount of implementation details.
    • I’ve had a lot of luck covering line-of-business web apps with mostly subcutaneous tests against the MVC controllers, with a smattering of unit tests to check conventions and test really complex logic and I typically see how far I can get without writing UI tests, but when I do I test high-value scenarios or complex UIs.
  • What is a unit test anyway? Everyone seems to have a different definition!
  • How do I get feedback as fast as possible – reducing feedback loops is incredibly important.
    • Follow Jimmy’s advice and focus on writing as many tests that are as fast as possible rather than worrying about whether a test is a unit test or integration test.
    • Be pragmmatic though, you might get adequate speed, but a higher level of confidence by integrating your tests with the database for instance (this has worked well for me)
  • How much time/effort are we prepared to spend testing our software and what level of coverage do we need in return?
    • I think it depends on the application – the product owner, users and business in general will all have different tolerances for risk of something going wrong. Do the minimum amount that’s needed to get the amount of confidence that is required.
    • In general I try and following the mantra of “challenge yourself to start simple then inspect and adapt” (thanks Jess for helping refine that). Start off with the simplest testing approach that will work and if you find you are spending too long writing tests or the tests don’t give you the right confidence then adjust from there.
  • How do I keep my tests maintainable and how do I reduce the number of tests that break when I need to make a change to the codebase?
    • Focus on removing implementation details from tests. Be comfortable testing multiple classes in a single test (use your production DI container!).
    • Structure the tests according to user behaviour – they are less likely to have implementation details and they form better documentation of the system.
  • How do I make sure that my tests give me the maximum confidence that when the code is shipped to production it will work?
    • Reduce the amount of mocking you use to the bare minimum – hopefully just things external to your application so that you are testing production-like code paths.
    • Subcutaneous tests are a very good middle ground between low-level implementation-focused unit tests and slow and brittle UI tests.
  • When should I be mocking the database, filesystem etc.
    • When you need the speed and are happy to forgo the lower confidence.
    • Also, if they are external to your application or not completely under your application’s control e.g. a database that is touched by multiple apps and your app doesn’t run migrations on it and control the schema.
  • How do I ensure that my application is tested consistently?
    • Come up with a testing strategy and stick with it. Adjust it over time as you learn new things though.
    • Don’t be afraid to use different styles of test as appropriate – e.g. the bulk of tests might be subcutaneous, but you might decide to write lower level unit tests for complex logic.

In closing, I wanted to show a couple of quotes that I think are relevant:

Fellow Readifarian, Kahne Raja recently said this on an internal Yammer discussion and I really identify with it:

“We should think about our test projects like we think about our solution projects. They involve complex design patterns and regular refactoring.”

Another Readifarian, Pawel Pabich , made the important point that:

“[The tests you write] depend[s] on the app you are writing. [A] CRUD Web app might require different tests than a calculator.”

I also like this quote from Kent Beck:

“I get paid for code that works, not for tests, so my philosophy is to test as little as possible to reach a given level of confidence.”

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