Code Retreat in Wroclaw

October 21, 2010

Next weekend there’s a Code Retreat in Wroclaw: I’ll be there so If you want to cut some code together retreat with us =)

Developer! rid your wip!

October 14, 2010

I’m big on eliminating waste, I’m big on minimizing Work In Progress (WIP).

Here’s my story: a colleague asked me to pair with him because he broke the application and he didn’t know why. So we sat together. My first question was:

– “Did the app work before you made your changes?”
– “Yes”
– “Ok, show me the changes you made”

I saw ~150 hundred unknown files, ~20 modified or added files. I said:

– “That’s a lot of changes. I bet you started doing too many changes at once so you ended up with a lot of WIP. Can we revert all the changes you made?”
– “Errr… I guess so. I know what refactoring I wanted to do. We can do it again”
– “Excellent, let’s clean your workspace now”

We reverted the changes. We also discovered that there were some core “VCS ignores” missing (hence so many unknown files in the working copy). We fixed that problem by adding necessary “VCS ignores”. I continued:

– “Ok, the working copy is clean and the application works OK. Let’s kick off the refactoring you wanted to do. However this time, we will do the refactoring in small steps. We will keep the WIP small by doing frequent check-ins on the way.”
– “Sounds good”

Guess what. We didn’t encounter the initial problem at all. We completed the refactoring in ~1 hour doing several check-ins in the process. Previous attempt to the refactoring took much more time due to few hours spent on debugging the issue.

Here’s my advice for a developer who wants to debug less & smile more:

  1. Understand what is your work in progress; keep WIP under control; keep it small.
  2. Develop code in small steps.
  3. Keep your workspace clean, avoid unknown or modified files between check-ins.

subclass-and-override vs partial mocking vs refactoring

January 13, 2009

Attention all noble mockers and evil partial mockers. Actually… both styles are evil :) Spy, don’t mock… or better: do whatever you like just keep writing beautiful, clean and non-brittle tests.

Let’s get to the point: partial mocking smelled funny to me for a long time. I thought I didn’t need because frankly, I haven’t found a situation where I could use it.

Until few days ago when I found a place for it. Did I just come to terms with partial mocks? Maybe. Interestingly, partial mock scenario seems to be related with working with code that we don’t have full control of…

I’ve been hacking a new feature for mockito, an experiment which suppose to enhance the feedback from a failing test. On the way, I encountered a spot where partial mocking appeared handy. I decided to code the problem in few different ways and convince myself that partial mocking is a true blessing.

Here is an implementation of a JunitRunner. I trimmed it a little bit so that only interesting stuff stayed. The runner should print warnings only when the test fails. The is wrapped in a separate method so that I can replace this method from the test:


How would the test look like? I’m going to subclass-and-override to replace runTestBody() behavior. This will give me opportunity to test the run() method.


It’s ugly but shhh… let’s blame the jUnit API.

The runTestBody() method is quite naughty but I’ve got a powerful weapon at hand: partial mocking. What’s that? Typically mocking consist of using a replacement of the entire object. Partial stands for replacing only the part of real implementation, for example a single method.

Here is the test, using hypothetical Mockito partial mocking syntax. Actually, shouldn’t I call it partial stubbing?


Both tests are quite similar. I test MockitoJUnitRunner class by replacing the implementation of runTestBody(notifier). First example uses test specific implementation of the class under test. Second test uses a kind of partial mocking. This sort of comparison was very nicely done in this blog post by Phil Haack. I guess I came to the similar conclusion and I believe that:

  • subclass-and-override is not worse than partial mocking
  • subclass-and-override might give cleaner code just like in my example. It all depends on the case at hand, though. I’m sure there are scenarios where partial mocking looks & reads neater.

Hold on a sec! What about refactoring? Some say that instead of partial mocking we should design the code better. Let’s see.

The code might look like this. There is a specific interface JunitTestBody that I can inject from the test. And yes, I know I’m quite bad at naming types.


Now, I can inject a proper mock or an anonymous implementation of entire JunitTestBody interface. I’m not concerned about the injection style because I don’t feel it matters that much here. I’m passing JunitTestBody as an argument.


Let’s draw some conclusions. In this particular scenario choosing refactoring over partial mocking doesn’t really push me towards the better design. I don’t want to get into details but junit API constrains me a bit here so I cannot refactor that freely. Obviously, you can figure out a better refactoring – I’m just yet another java developer. On the other hand, the partial mocking scenario is a very rare finding for me. I believe there might be something wrong in my code if I had to partial mock too often. After all, look at the tests above – can you say they are beautiful? I can’t.


  • I cannot say subclass-and-override < partial mocking
  • not always refactoring > subclass-and-override/partial mocking
  • partial mocking might be helpful but I’d rather not overuse it.
  • partial mocking scenario seems to lurk in situations where I cannot refactor that freely.

Eventually, I chose subclass-and-override for my implementation. It’s simple, reads nicer and feels less mocky & more natural.

should I worry about the unexpected?

July 12, 2008

The level of validation in typical state testing with assertions is different from typical interaction testing with mocks. Allow me to have a closer look at this subtle difference. My conclusion dares to question the important part of mocking philosophy: worrying about the unexpected.

Let me explain by starting from the beginning: a typical interaction based test with mocks (using some pseudo-mocking syntax):


Typical interaction based test

Here is what the test tells me:

When you read the article
then the should be called
and NO other method on the reader should be called.

Now, let’s have a look at typical state based test with assertions:


Typical state based test

Which means:

– When you read the article
– then the article should be read.

Have you noticed the subtle difference between #1 and #2?

In state testing, an assertion is focused on a single property and doesn’t validate the surrounding state. When the behavior under test changes some additional, unexpected property – it will not be detected by the test.

In interaction testing, a mock object validates all interactions. When the behavior under test calls some additional, unexpected method on a mock – it will be detected and UnexpectedInteractionError is thrown.

I wonder if interaction testing should be extra defensive and worry about the unexpected?

Many of you say ‘yes’ but then how come you don’t do state based testing along this pattern? I’ll show you how:


State based test can detect the unexpected!

Which means:

– When you read the article
– then the article should be read
– and no other state on the article should change.

Note that the assertion is made on the entire Article object. It effectively detects any unexpected state changes (e.g: if read() method changes some extra property on the article then the test fails). This way a typical state based test becomes extra defensive just like typical test with mocks.

The thing is state based tests are rarely written like that. So the obvious question is how come finding the unexpected is more important in interaction testing than in state testing?

Let’s consider pros & cons. Surely detecting the unexpected seems to add credibility and quality to the test. Sometimes however, it just gets in the way, especially when doing TDD. To explain it clearer let’s get back to the example #3: the state based test with detecting the unexpected enabled. Say I’d like to test-drive a new feature:


Test-driving new feature

I run the tests to find out that newly added test method fails. It’s time to implement the feature:

Adding new feature

I run the test again and the new test passes now but hold on… the previous test method fails! Note that the existing functionality is clearly not broken.

What happened? The previous test detected the unexpected change on the article – setting the date. How can I fix it?

1. I can merge both test methods into one which is probably a good idea in this silly example. However, many times I really want to have small, separate test methods that are focused around behavior. One-assert-per-test people do it all the time.

2. Finally, I can stop worrying about the unexpected and focus on testing what is really important:

public shouldSetReadDateWhenReading() {;
assertEquals(today(), article.getReadDate());

public shouldReadArticle() {;

Ok, I know the example is silly. But it is only to explain why worrying about unexpected may NOT be such a good friend of TDD or small&focused test methods.

Let’s get back to mocking.

Most mocking frameworks detect the unexpected by default. When new features are test-driven as new test methods, sometimes existing tests start failing due to unexpected interaction errors. What happens next?

1. Junior developers copy-paste expectations from one test to another making the test methods overspecified and less maintainable.

2. Veteran developers modify existing tests and change the expectations to ignore some/all interactions. Most mocking frameworks enables developers to ignore expectations selectively or object-wise. Nevertheless, it is still a bit of a hassle – why should I change existing tests when the existing functionality is clearly not broken? (like in example #4 – functionality not broken but the test fails). The other thing is that explicitly ignoring interactions is also a bit like overspecification. After all, to ignore something I prefer just not to write ANYTHING. In state based tests if I don’t care about something I don’t write an assertion for that. It’s simple and so natural.

To recap: worrying about the unexpected sometimes leaves me with overspecified tests or less comfortable TDD. Now, do I want to trade it for the quality? I’m talking about the quality introduced by extra defensive test?

The thing is I didn’t find a proof that the quality improved when every test worried about the unexpected. That’s why I prefer to write extra defensive tests only when it’s relevant. That’s why I really like state based testing. That’s why I prefer spying to mocking. Finally, that’s why I don’t write verifyNoMoreInteractions() in every Mockito test.

What do you think? Have you ever encountered related problems when test-driving with mocks? Do you find the quality improved when interaction testing worries about the unexpected? Or perhaps should state testing start worrying about the unexpected?

10 rules of (unit) testing

January 31, 2008

There you go, those are my 10 rules of (unit) testing. It’s nothing exciting, really. Everyone is so agile these days. Are you agile? I bet you’d say: I was born agile.


Here I come with my own 10 commandments. I came up with those while doing research on mock frameworks (haven’t you heard about Mockito, yet? it’s the ultimate tdd climax with java mocks). I browsed so much of our project’s test code that I feel violated now (codebase is nice, though).

  1. If a class is difficult to test, refactor the class. Precisely, split the class if it’s too big or if has too many dependencies.
  2. It’s not only about test code but I need to say that anyway: Best improvements are those that remove code. Be budget-driven. Improve by removing. The only thing better than simple code is no code.
  3. Having 100% line/branch/statement/whatever coverage is not an excuse to write dodgy, duplicated application code.
  4. Again, not only about test code: Enjoy, praise and present decent test code to others. Discuss, refactor and show dodgy test code to others.
  5. Never forget that test code is production code. Test code also loves refactoring.
  6. Hierarchies are difficult to test. Avoid hierarchies to keep things simple and testable. Reuse-by-composition over reuse-by-inheritance.
  7. One assert per test method is a bit fanatical. However, be reasonable and keep test methods small and focused around behavior.
  8. Regardless of what mock framework you use, don’t be afraid of creating hand crafted stubs/mocks. Sometimes it’s just simpler and the output test code is clearer.
  9. If you have to test private method – you’ve just promoted her to be public method, potentially on different object.
  10. Budget your tests not only in terms of lines of code but also in terms of execution time. Know how long your test run. Keep it fast.

Number #1 is my personal pet. Everybody is so test-driven but so little really care about #1 in practice. Best classes, frameworks or systems offer painless testing because they’re designed & refactored to be testable. Let the code serve the test and you will produce delightful system.

Number #7 is a funny one (‘Cos we need a little controversy). The whole world rolls in the opposite direction. Maybe I just don’t get it… yet. Or maybe it’s because I paired with young one-assert-per-test guy once. He cunningly kept writing test methods to check if constructor returns not-null value. If I had to play this game and chose my one-something-per-test philosophy I’d steal MarkB’s idea: one-behaviour-per-test. After all, It’s all about behavior…

is private method an antipattern

January 5, 2008

After a conversation with my friend and after a cursory google search, here are my thoughts:

Private method a smell’ seemed to be ignited with the birth of TDD. Test-infected people wanted to know how to test their private methods. Gee… it’s not easy so the question evolved from ‘how‘ into ‘why‘: Why to test private method? Most of TDDers would answer instantly: don’t do it. Yet again TDD changed the way we craft software and re-evaluated the private methods :)

Clean SpringTest-driven software tends to have less private methods. Shouldn’t we have a metric like: private methods to public methods ratio? I wonder what would be the output for some open source projects (like spring – famous for its clean code).

So, is private method an antipattern or not!?

If the class is so complex that it needs private methods, shouldn’t we aim to pull some of that complexity into its own class?

The code never lies: We looked at several distinctly big classes and put their private methods under magnifying glass. Guess what… Some of the private methods where clear candidates to refactor out to separate class. In one case we even moved whole private method, without a single change, into separate class ;)

Privacy may be an antipattern. Look at your private methods – I bet some of them should be public methods of different objects.

consistency over elegance

December 29, 2007

Usually developers spend more time on reading code rather than writing code. Consistency makes the code more readable.

Is it better to do things consistently wrongly than erratically well? Maybe not in life but when it comes to software. Here are my ratings:

:-D consistently well
:-) consistently wrongly
:-| erratically well
:-( erratically wrongly

Consistency wins.

Sometimes particular anti-pattern consistently infests whole application. There is no point in throwing bodies in refactoring it because the cost may be little compared to the gain. Anti-pattern may be well-known and in general not extremely harmful. Refactoring it in one place may seem decent but introduces inconsistency with all the other places. I value overall consistency over single-shot elegance.

There’s no rule without exception, right? Sometimes the goal is to implement something in completely different way, to implement an eye-opener, to create “the new way”. Then one could relay on distributed-refactoring spirit of the team and let others join refactoring feast. If the spirit evaporated :(, one could always make using “the old way” deliberately embarrassing or just frikin’ difficult.

Consistency rule helps in all those hesitations a developer has on daily basis. Ever felt like two-headed ogre from Warcraft?

“This way, no that way!” – the heads argue.

Yes, you can implement stuff in multiple ways… My advice is: know your codebase and be consistent. Choose the way that was already chosen.

Being consistent is important but not when it goes against The Common Sense. Obviously ;)