Michael Feathers

Video Interview I did for InformIT

Last year, at SD Best Practices, I was asked to do a video interview on unit testing and legacy code.  I was mentally tired at the time and Ted Neward (who was interviewing) had been interviewing people all day, so shuddered to ever see it released.

Turns out, it's surfaced.  I wish I'd elaborated on a few points, but I think it turned out okay.

The interview is here and there are a bunch of other interviews in the series here.. interviews with Bjarne Stroustrup, Scott Meyers, Joshua Bloch and many others.

The Deep Synergy Between Testability and Good Design

Join any discussion about unit testing and there's one question that will invariably come up: how do you test private methods?

There are a number of answers.  Some people advocate increased visibility.  They say that if you feel that you must test a private method, it's really no great sin to make it protected, public or package private in order to make it testable.

Other people say that you can use special tools to access private methods.  In Java, at least, you can quite easily rig something up with reflection to give you any kind of access you'd like.

These are "okay" answers, but really they are missing something.  When I write tests and I have the urge to test a private method, I take it as a hint.   The hint tells me that my class is encapsulating so much that it has ceased to be "understandable" by tests through its public interface.  I listen to the hint, and factor my design differently.  Usually, I end up moving the private method (and possibly some methods around it) to a new class where it can be non-private and accessible to tests.

Aiming for testability actually changes your design.

But, is that good?

The answer for me, so far, has been yes.  There appears to be a synergy between testability (at the unit level) and good design.  If you aim for testability and make some good choices, design gets better.  If you aim for good design, your design becomes more testable. 

In the end, it all comes down to cohesion and coupling.  If classes are deeply coupled with their neighbors, it is hard to control them in a test or observe them independently.  If a class isn't cohesive, it may have some logic which is not easily exercisable through its public interface.

It seems that reverse is true also.  Classes which are hard to instantiate and use in a test harness are more coupled than they could be, and classes with private methods that you feel the urge to test, invariably have some sort of cohesion problem: they have more than one responsibility.

I suspect that some people reading this might think it is a load of wishful thinking, or that this synergy between testability and good design is just a hypothesis without much to back it.  All I can say is that in the community of people doing test-driven development there are a number of people who have found that this question of testing private methods doesn't come up much in their practice.  They target both testability and good design and find that both goals nurture each other.

Is the synergy real?  I think it is.  When a bit of functionality is not easily understood  by a test at the public interface, the chances of it being easily understood by a human are ridiculously low.  And, if there is any universal baseline for good design it has to be understandability.

So, having said all of this, I end this blog with a challenge: Can anyone come up with an example in which there is a private method that they feel that they have to test.. something that they don't feel comfortable testing through the public interface of the class, but which can't be made testable with a better design?

Soft Sciences

The other day, I was at the airport in Madrid, lurking around a bookstore trying to find something to read on the long flight home.  The store had a well-sized English language section, but it was stocked mostly with crime and romance novels.  It didn't have any of the history or pop science that you see in larger American airports.  Usually, I settle for one of those.  I bought my copies of Blink and Freakonomics in airports.  They are just the sort of reading that I like after a long gig.. books of ideas that really don't have anything to do with software development, although I often end up relating them back to development out of habit.

I kept looking and I eventually ran across a set of five paperback novels by a writer named Paul Auster.  I'd never heard of him before, but I was tempted to buy all of them.  Each of the books had a back page description that intrigued me, and the reviewer comments looked great also.  I thought it over.  Five books was a bit much, so I settled for two and read one, Oracle Night, on the flight home. 

Oracle Night is the tale of a writer, who after a near-death experience, buys a notebook and starts to write a story about a man who decides to abandon his life and start a new one after a similar experience.  As he writes in his notebook, his own life becomes stranger and eventually starts to shift out of control in counterpoint with the story that he is writing.

The book was great.  It had all of the elements that I've been looking for in fiction lately.  A complicated plot, crisp writing, mystery and a philosophical edge.  When I got home, I looked up Paul Auster in wikipedia and this sentence leapt out at me "Two strong elements in Paul Auster's writing are Jacques Lacan's psychoanalysis and the American transcendentalism of the early to middle 19th century.."

It was then that I realized that something nutty was going on.  This was the fourth time over the past few weeks, that I'd discovered that this guy, Jacques Lacan, was tied into something that I'd seen.

Before I'd gone off to Madrid, I caught a few minutes of a documentary about a man named Slavoj Žižek.  Slavoj is a contemporary Solvenian post-modernist and cultural critic.  In the documentary, he said some interesting things about world affairs, things about the resurgence of nationalism and racism that we see in various parts of the world now that some of the older programs of the 20th century have lost their punch (communism) or succeeded (global capitalism).  He tied it back to a world view that he claimed came from Lacan.  Out of curiosity, I ordered a few books by Žižek and Lacan from Amazon.

The third Lacan connection is a bit weirder.  On reddit, I'd run across a reference to a painting called L'Origine du Monde (The Origin of the World) by Gustave Coubert.  Be careful about googling that one.   L'Origine du Monde is a graphically sexual painting that scandalized France in the 19th century.  And, it turns out, that before it found its final resting place in a French museum, it was owned by Lacan.

The last connection came when I started flipping through a book about Lacan.  It turns out that he had worked with  a psychoanalyst named W.R. Bion who'd done some of the earliest work on group dynamics. 

So, I have to figure out who this Lacan character is and why I keep running into him.  What I've read of his work so far is interesting.  Lacan extended the ideas of Freud, making the case that the unconscious is structured like a language.  We form our identity in a strange dynamic between the symbols that we use, our ideas about them, and our experience.  He saw psychosis and neurosis as breakdowns in the mind's ability to accept or utilize certain symbols.

There's nothing quite like reading the work of psychoanalysts.  Freud, Jung, Lacan, Bion, etc.  Many people claim that what they were doing was too soft to be science, and I think they have a point.   But, on the other hand, if you take the point of view that they were doing something very difficult, trying to understand the basis of emotional experience and motivation in much the same way as physicists try to find elementary particles, it's easier to appreciate what they were doing.  Physicists have tools.  They can measure.  The things that these early psychoanalysts were interested in weren't measurable.  All they had was observation and inference.  It's like the tale of the blind men and the elephant.  Every blind man tells you something different about what what he's felt, but if you stand back, you might get a sense of the whole elephant.

Anyway, for me this dive into Lacan is interesting.  It gets me out of the binary.  There are thousands of views of human nature.  There's truth in all of them, yet none of them are true.  That's tough to deal with if you want certainty.  But, really, what's fun about certainty?