Tag Archives: Unit-Testing

The LJC ran it’s ever-popular annual Open Conference on Saturday 23rd November, and this was the first time I’ve made it along. To say I was impressed was an understatement, and I’ll try and capture some more thoughts in a later blog post, but for the moment I wanted to share the slides from the main presentation I delivered “Chuck Norris Doesn’t Need DevOps”


Can’t see the presentation slides? Please click here

The original pitch for the talk was as follows:

“We all hear the term “DevOps” being thrown around on a daily basis, but what does it actually mean? With a little help from everyone’s favourite 80’s action hero, we’ll undergo a whistle-stop tour of the philosophy, culture and tooling behind this buzzword, specifically aimed at Java Developers.

We’ll also look at a real-world case study from Instant Access Technologies Ltd, and explore the key role that DevOps has played during a successful upgrade of the epoints customer loyalty platform to support increasing traffic. The core discussion will focus on the challenges encountered as we moved from a monolithic app deployed into a data centre on a ‘big bang’ schedule, to a platform of loosely-coupled components, all being continuously deployed into the Cloud.”

Thanks to everyone who attended my presentation! The feedback was most welcome, and the questions were great. If anyone wants to add anything further than please feel free to comment, email or tweet at me!

Practical Unit Testing with TestNG and Mockito – by Tomek Kaczanowski


TL;DR This is an essential book on Unit Testing for both novice and experienced Java developer alike. Practical Unit Testing provides a well-paced and logical introduction into the world of Unit Testing, and also offers the more experienced practitioners a discussion on topics such as defining what to test and verify, how to write high-quality and maintainable tests, and also when (shock horror!) not to test. This book provides a plethora of examples and is extremely pragmatic in it’s delivery of testing in the real world. I would also strongly recommend this book to any JUnit fans that haven’t experimented with TestNG lately – you might be surprised what this framework now offers!

Practical Unit testing is divided into five primary sections: ‘Developer’s Tests’, ‘Writing Test’, ‘Hints and Discussion’, ‘Listen and Organise’ and ‘Make them better’. It’s worth mentioning here that this flavour of the book strongly focuses on using TestNG and Mockito (there is a JUnit flavoured version, Practical Unit Testing with JUnit and Mockito). As mentioned above, if you haven’t played with TestNG lately, I would recommend that you do (with this book by you side), as the framework has developed rapidly over the past few years into a genuine competitor against JUnit.

Section 1, ‘Developer’s Tests’, begins by discussing motivations and the core methodology behind testing in general. Unit testing is then defined and the basic concepts introduced to the reader. Section 2 begins by getting the reader to write their first tests, and introduces key concepts such as assertions and parameterised tests.

Section 2 of the book continues with Chapter 4, which introduces the reader to Test Driven Development (TDD), and IMHO this chapter should be read by all Java developers. The author presents an excellent discussion on when to write tests, the ‘rhythm’ of TDD and the benefits offered, and also provides concrete examples. This chapter even covers when not to use TDD, which I know can be heresy to some advocates, but as a long time practitioner of TDD I can relate to points made by the author in this chapter.

As with any technique (or philosophy) as powerful as TDD it is easy to become dogmatic about the subject, and ultimately forgot that not every problem can be solved with a single approach or solution. Paraphrasing the author, he suggests problem areas with applying TDD can include not having a good knowledge of the problem domain, not understanding the technologies, and when working on legacy code. In my experience, I have made several mistakes with applying TDD in the areas identified, and so the author’s cautions should be well received (on a related topic, I can highly recommend Working Effectively with Legacy Code (Robert C. Martin) when dealing with testing legacy code)

Next is very useful discussion Mocks, Stubs and Spies, which is obviously focused on Mockito (which is currently my Mocking framework of choice). As with all the concepts discussed in this book, the example code provided is very useful and of high quality. On a related topic, I would definitely recommend a read of the Mockito website in addition to the this chapter, as the website includes a vast array of examples, and is also updated often.

Section 3 of the book kicks off with Chapter 6, ‘Things You Should Know’, and this chapter is again essential reading. In fact I would go so far to say that this part of the book is worth the entry fee alone – it covers a lot very interesting topics, such as knowing what to test, isolating code under test, making tests timely, using external data and dealing with concurrency. It also discusses what the author refers to as ‘points of controversy’, such as limiting multiple assertions per test (the logical assertions debate) and private method testing.

The remaining two sections of the book focus on getting feedback from tests (and what to do with it), how to organise your tests, and also how to write maintainable high-quality tests. This was an often overlooked topic in a lot of the earlier TDD books, and the often (unspoken) implication was that test code doesn’t have to be as high-quality as ‘production’ code, which is obviously a complete fallacy. In my experience poorly written (and brittle) tests can often slow development down considerably, and this ultimately leads to tests being either removed or ignored…

In summary, this is an essential purchase for any Java developer serious about testing and TDD. For some reason, this book appears to be under the radar to a lot of TDD advocates, and I’m not sure why. The current favourite TDD book, of which I am also a huge fan of, is Effective Unit Testing: A guide for Java developers, and I believe this TestNG-focused book is a great complement to the JUnit-focused work presented in Effective Unit Testing. Practical Unit Testing provides a great introduction for developers new to TDD, and also offers experienced TDDers plenty to think about. The book is well-paced and logical in it’s approach, and provides a comprehensive approach to writing useful, high-quality and maintainable tests.

Click here to buy Practical Unit Testing with TestNG and Mockito on Amazon UK (This is a sponsored link. Please click through and help a fellow developer buy some more books!)

A fellow LJCer and TDD/BDD advocate has recently started developing an application using the ever-popular Spring stack, and he asked my advice on how best to implement a Test-driven methodology within this context. I started typing an email back in response, but then it suddenly occurred to me that this might be useful for other people as well… So here it is – I hope it helps 🙂


The rest of this post assumes the following:

  • Applications will be implemented in Java using the following components of the Spring stack: Core, MVC, Data, Security etc BUT we won’t be covering Spring Integration or Batch (although the recommended testing frameworks and tools can be quite similar I find that the techniques for testing these components can be quite different, and so this will have to wait until another blog post :))
  • ‘End-users’ will interact with the developed application(s) via a web-based UI and/or HTTP-based API (typically, but not exclusively REST-like)
  • For production an external datastore will be utilised to persist long-lived state within the application. We assume that you will want to test how your application interacts with this too.
  • We will not cover testing via remote or embedded containers, other than using a simple in-memory servlet container such as Jetty to deploy the entire packaged application. Frameworks such as Arquillian offer some really cool features that allow Unit testing against real (embedded) containers such as Tomcat, GlassFish and JBoss Application Server. This is achieved by providing mechanisms to simulate production-like packaging (“ShrinkWrapping“) and deployment of an arbitrary sub-set of components (down to the Class-level) for testing within the embedded container, all via your favourite testing framework such as JUnit.

General Recommendations

If you’re new test-driven development I recommend the following books:

  • Effective Unit Testing: A guide for Java developers – This is a great (and up to date) introduction to all key concepts and technologies within Java-based unit testing. This book not only covers motivations and methodologies, but also how to write ‘good’ tests that are expressive and maintainable etc, and also advice on choosing the most appropriate technique for each use case.
  • Practical Unit Testing with JUnit and Mockito and/or Practical Unit Testing with TestNG and Mockito. These are both great books that contain a wealth of practical examples on how to test Java applications, and also discusses the why and how of TDD. Both books are very similar and differ primarily in the framework used to drive the tests. My advice is to buy the TestNG version in combination with ‘Effective Unit Testing’ (which is primarily focused on JUnit), as it’s great to know the differences and strengths/weaknesses of the two most popular Java-based testing engines.
  • Growing Object-Oriented Software, Guided by Tests (Beck Signature) – this is one of the classic TDD books, and it discusses all of the high-level concepts and motivations of Test-driving application design. This book also provides a great practical example of how to use the prescribed methodology by detailing the construction and evolution of an entire application based on an auction website.
  • There are a few books written about Unit testing JavaScript, and although I haven’t had chance to read them all I do recommend Testable JavaScript

Testing the Core

Unit Testing

Purpose: The core of your application models the problem you are trying to solve, and typically contains domain-specific representations and associated ‘business’ rules which you are primarily responsible for writing (i.e. the opportunity to re-use third-party code here is somewhat limited).

Accordingly it is easy to argue that this code should be well tested – not only are the components you implement here likely to be unique, but you want to be sure they behave as expected before wiring them up to frameworks that offer boilerplate functionality, such as persistence. Well written tests here can also ‘document’ your code (and associated functionality) at the micro level.


  • JUnit / TestNG – de facto frameworks for running Java tests. I like to run these as part of my Maven build process via the surefire plugin
  • Spock – an awesome Groovy-based testing and specification framework. If you haven’t heard of it stop reading right now and go visit the webpage. Seriously. Now check out the Spock Basics page. How awesome is that?? 🙂 And it plays well with Spring too!
  • Mockito – my favourite mocking framework. Others do exist, but I find Mockito strikes a great balance betweeen ease of use, expressivity and maintainability
  • PowerMock – a great extension to Mockito for use when you face a difficult situation that Mockito can’t cope with, such as mocking an old library that relies on static methods, or mocking private or final methods, or mocking object instantiation. My advice is to always double and triple-check your component design when you start reaching for PowerMock – often the desire to use PowerMock indicates a testing ‘smell’, and may indicate that your component design should be improved, or the manner in which your code interfaces with external dependency could be enhanced. For example, rather than mocking a third-party library’s static constructor method, could you not hide this method call behind your own interface (following the decoractor/adapter pattern) which will facilitate easier mocking?
  • ConcurrentUnit – a great utility framework for the difficult task of testing concurrency within components
  • Make-it-easy – a great little framework for creating Test Data builder (the concept of which comes from the aforementioned ‘Growing Object-Oriented Software, Guided by Tests)
  • junitparams – a great framework for augmenting JUnits parameterised testing (or as the creator states – ‘Parameterized tests that don’t suck’)


  • Isolate Classes and components under test. Unit tests should be focused on testing small units of work, and therefore have minimal dependencies (or dependencies should be mocked)
  • Create test cases that cover all paths through the code, not just the happy path
  • Create tests the replicate edge cases
  • Use the power of parameterised tests to facilitate rapid addition of data-driven test cases as they are discovered


  • Write trivial tests just to increase unit test coverage
  • Create brittle tests that break with the slightest change to your code i.e. if your using more than 10 lines of code to set up your mocks and expectations then you may be doing something wrong
  • Test getters and setters, unless they contain logic
  • Directly test any interaction with the underlying OS (file, network etc), a datastore, or any container/server. This interaction should be mocked at this level of testing

Plugging it together

Integration Tests – Persistence Layer

Purpose: Think Unit testing for your persistence or DAO layer, but here you want to simulate behaviour offered by an external resource, rather than mocking this functionality.


  • All the Unit Testing tools mentioned above plus…
  • Utilise Spring’s @ContextConfiguration  to manage the wiring of dependencies together, such as an EntityManager or MongoOperations, and AbstractTransactionalJUnit4SpringContextTests to manage running the tests with well-defined transaction semantics
  • Embedded (in-memory) versions of your chosen datastore e.g.
    • H2 – A great embedded SQL datastore, and in 99% of standard use cases behaves like MySQL (although Your Mileage May Vary…)
    • Embedded MongoDB – for all your MongoDB datastore needs (or for older versions of MongoDB, pre 2.9, check out another project I contributed to SDFongo)
    • Embedded Solr via ZoomInfo’s InProcessSolrServer, and updated by me (shameless self-plug! 🙂 )
    • ActiveMQ – run as embedded and non-persisting


  • Assert that entities persist as you expect them. I’ve lost count of the number of times I’ve incorrectly configured XToMany JPA annotations which resulted in incorrect cascading operations to child entities.
  • Aim to keep test execution time reasonably small.
  • Test all public methods exposed on the DAO/repository interface
  • Create harnesses that allow the loading of pre-canned test data. Think executeSqlScript() from Spring’s AbstractTransactionalJUnit4SpringContextTests
  • Destroy (or delete) data at the end of each test in order to prevent previous test data from influencing results. This is especially important if your chosen testing framework doesn’t guarantee the order in which tests are executed!


  • Overly duplicate coverage from the Unit tests i.e. most business logic will call the persistence layer to load data, process this, and call the persistence layer again to save the results. Tests at this level only need to focus on the load and save
  • Test every conceivable permutation of data
  • Chain too many operations together – this should be covered by service-integration tests or end-to-end tests

Coming in Part 2…

I’ll try and post Part 2 soon, and this will cover topics such as Service-level Integration testing, Web-based testing and API testing. Part 3 will cover end-to-end (E2E) testing and BDD.