Test Automation Basics – Levels, Pyramids & Quadrants

This post started life in my series on hexagonal architecture, but it got too unwieldy & not directly related to the topic so here it is in all its own glory.

This post is now a brief introduction to my understanding of test automation, the test automation pyramid & testing quadrants and is used as a reference for the hexagonal architecture series.

James Crisp Test Pyramid

Thisย  test automation & the associated test levels. This section will cover the test levels & bit on Brian Maricks Testing Quadrants (which I’ve found really useful for testing in an agile environment)

I subscribe to the idea of the automation pyramid (taken from James Crisps post on test automation). The image above shows the test levels in a pyramid shape & demonstrates the relationships between amount of tests at each test level in a test suite.

A very thorough analysis on the test automation pyramid can also be found in The Tar Pit.

The main idea is that you want more unit tests than any other level of test because they:

  • test the behaviour of the class / component rather than its implementation
  • have no dependencies on other classes / components
  • are easy to write & maintain (due to their independence)
  • are quick to run

This makes them the most cost efficient way of testing of individual or closely related classes, but obviously they do not provide enough coverage to satisfy the development team of the confidence of the code.

So to increase coverage, we move up to integration tests which:

  • test the integration between components / features / external 3rd party services
  • are dependant on the other components / features / external 3rd party services being available & stable enough to execute tests against.
  • ensure dependencies of the system being developed continue to work as expected
  • are slower than unit tests to run, but faster than acceptance tests to run

Up until this point, the tests are largely technology focused (taken from Brian Maricks Testing Quadrants which I’ve found really useful for testing in an agile environment – more on this later. Lisa Crispin covers it well in her book & in this test planning presentation) – that is they serve the development team in proving the business logic & providing confidence that that logic has not been compromised.

The top of the triangle sees the acceptance (GUI) tests, of which there are the fewest number of tests in test suite. Acceptance tests are:

  • a tool for conversing with business stakeholders (as they are generally written in human-readable language)
  • a means of knowing when we’re done (developing a component / feature)
  • checking the UI by actually clicking buttons on that UI
  • High dependency on other components / features
  • Brittle – easily broken if the UI changes
  • Slowest of the 3 automated test levels to run

So if acceptance tests are slow & brittle, why do we go to the effort of writing them? Because they are the main tool for driving conversation between the development team & business stakeholders. The tests are generally examples of the requirements as specified by the business stakeholders so they get a feel for stable the code is.

This is the automation pyramid. It has been added to by Alister Scott who introduces the concept of manual testing:

ideal-automated-testing-pyramid-Alister-Scott

He also shows the intention of the tests in each level in this post responding to James Crisps original automation pyramid post:

business-technology-automated-testing-pyramid-alister-scottWith the “all seeing eye” at the top of the pyramid encompassing acceptance (GUI) & manual tests.

Take a close look at the small print: “Are we building the right system” &ย  “Are we building the system right” – This is a fundamental principle in “Agile Testing” where we (as Testers) shouldn’t just be focussing on finding bugs at the end of the development cycle. Instead we should be getting involved with the development as early as possible for example by helping to drive out requirements as & when they’re being worked on, not 6 weeks after a document has been put together (the end of yet another lifecycle). I go into more detail in my post responding to the Test is Dead movement of late 2011.

Anyway back to the test pyramid… Alister goes on to talk about a common problem in organisatons who use automation – the inverted pyramid, or ice-cream cone:

software-testing-ice-cream-cone-anti-pattern-Alister-Scott

this situation occurs where too much emphasis is placed on automated GUI & manual tests which may occur for numerous reasons such as lack of experience in writing lower level tests or working with leagcy code.

As I mention previously, a tool I’ve found very useful in determining which tests to run & what value they add is Brian Maricks Testing Quadrants:

Lisa Crispins representation of testing quadrants

You can see examples of the Business Facing tests on the top half of the quadrant (the top half of the pyramid) & the Technology Facing tests on the bottom half of the quadrant (the bottom half of the triangle).

Click on the image to get more detail from Lisa on how to use the quadrant.

Marekj (@rubytester) has also provide a great slide deck explaining the quadrants

Its another way of visualising the test levels & I find it compliments the pyramid quite nicely. Certainly I’ll be using both the Pyramid & the Quadrant in my hexagonal architecture post.

UPDATE: Elizabeth Hendrickson has revisted the tested quadrants in her CAST 2012 keynote “The Thinking Tester, Evolved” & Markus Gartner has done a great write up on the Elizabeth’s new interpretation on his blog. I’ll need to revisit the quadrants myself when I get time to digest the video & Markus’ post.

UPDATE 2: Gojko Adzic is also re-thinking the testing quadrants model. Some good conversation on this post.

Some useful links:

Test Pyramid (Cohn – credited as being the originator of the pyramid in “Succeeding With Agile“)

Test Pyramid (Fowler)

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  • Olud

    interesting post here, How did you come up with the relative ratio of the amount of tests needed for each phase i.e 70%,20%,10%

    • Duncan Nisbet

      Thanks for stopping by Olud, I appreciate you taking the time comment.

      The image (& therefore the percentages) was taken from James Crisps website (clicking on the image takes you to his site).

      Unfortunately his site is unavailable at the moment, so I can’t see why he chose those percentages.

      For me, they merely serve as a rough indication for the division between each level – I don’t believe you could ever say that every project should have 70% unit tests, 20% integration & 10% acceptance tests.

      Cheers,

      Duncs

  • Hi Duncan,

    thank you for the interesting post. I also find that the test pyramid presents a good guideline for testing graphical applications. However, for applications with a non-graphical interface I am not so sure. The main critique of GUI tests is that they are slow, brittle and expensive to maintain. For such tests, it pays off to not have too many of them, and rather have intermediate Integration tests that don’t go through the GUI. However, what about testing a web service for instance? For the web service, an “acceptance test” would be to send HTTP requests and test the results. This probably has none of the drawbacks of a GUI tests – slowness, brittleness or high maintenance effort – so I would say it doesn’t pay off to apply the test pyramid here. I wrote a blog article about this and my (/our) experiences: http://www.getautoma.com/blog/the-test-hourglass. Maybe you’d like to check it out!

    Cheers,
    Michael
    http://www.getautoma.com

    • Duncs

      Hi Michael – thanks for stopping by & leaving your comment.

      Its great to see that you have a solution which is a better for your context.

      Its a valid point that I came from an assumed context – one of an enterprise web app & all the associated tiers underneath the web layer.

      Its good to know alternatives to models as you never know where your next testing challenge will come from!

      Duncs

    • DuncanNisbet

      Hi Michael – thanks your comment.

      It’s great to see that you have a solution which is a better fit for your context.

      It’s a valid point that I came from an assumed context – one of an enterprise web app & all the associated tiers underneath the web layer.

      It’s good to know alternatives to testing models as you never know where your next testing challenge will come from!

      Duncs

      P.S. keep me posted on my referral count to your blog ๐Ÿ˜‰

      • Hi Duncan,

        thanks for your reply ๐Ÿ™‚ Yes, I think it’s always interesting to keep other models in mind.

        Regarding the referral count: 1 so far, and I suppose that was you ๐Ÿ˜‰ I hope you liked the post!

        Cheers!
        Michael