Following a better path

I intend to follow a better path, now that @marlenac has brought it to my attention.

When you are able to condense your software expertise into a practice that takes <10min and a relative beginner can mimic, and repeating that exercise thousands of times brings fresh insight to everyone at every level, you can call it a code kata. -- @jtu

The good TDD exercises do offer fresh insights at many levels, but less face it; the creation of these exercises doesn't demonstrate a lifetime of mastery so much as a clever idea that survived a few rough drafts.  Maybe.

The time limit is a really interesting constraint -- much of my complaints with the TDD exercises that I've found is that the scope of them is much too brief; that an hour of exploration isn't enough time to have the problems that TDD purports to solve.


 

Refactoring Lessons at the Gilded Rose

The month, the local meetup took on a variant of the Gilded Rose kata.  As I was in a facilitator's chair,  I didn't get to explore any new ideas this time around.  So I decided to work through the exercise this evening.

In doing so, I picked up a couple interesting tricks from Intellij IDEA.

First, I learned that IntelliJ understands the idea of "run all tests in this package", which saves some of the headache of creating a regression suite when your tests are spread out across multiple files.

Second, I learned that IntelliJ can be quite clever about reducing predicates if it has a clear idea which invariant holds.  In various methods I introduced, an assert that described the preconditions for the Strings that were in scope allowed intellisense to remove a bunch of redundancy in the conditionals.

Either it wasn't entirely clever, or I made some bad choices in chosing which refactoring option to take when presented with a choice, but in a number of cases I ended up with ifs in front of empty blocks.  IntelliJ was also able to perform the refactoring to remove them, but I had to ask.


The grand strategy wasn't quite what I had expected it to be.  Back in the "Look, Ma, no hands" era, we tended to focus on micro refactorings, from which some Platonic ideal design would eventually emerge.  But for the Gilded Rose problem, the game seems to be to origami the code into a shape that intellisense recognizes.  So that means a bit of preparatory judo followed by swinging large blocks of code around so that the static code analysis can consider one domain problem at a time.

In short, instead of chasing a good design, I'm first chasing a design that the machine understands well enough to manipulate and simplify without requiring that I type anywhere near the complexity.  Let's face it, the carbonware is barely qualified to type at all -- its role is to point, and let the sand do the dirty work.

TDD: Safety in Numbers - a Bowling Game Adventure

Last night, I decided to work through a bowling game exercise, but it didn't quite turn out as I had expected.

The goal was eliminate duplication; how much intention revealing code could I introduce before moving onto the second test?

As suggested by Uncle Bob, I started with the degenerate case:

It is, of course, trivial to get this test passing. We simply hard code the required answer into the score method.

The step that I expected to follow was to immediately start introducing domain concepts, like frames, into the production code while there was still but a single test constraint in place.

And it was a very uncomfortable experience - I realized fairly quickly that a simple pass signal wasn't enough to give me confidence that the match I was introducing was actually manipulating the figures correctly -- not enough to give me confidence that I wasn't introducing silly fence post errors.

After discarding the work and contemplating the ceiling for a time, I decided that I was having trouble because zero is the additive identity -- I couldn't look at my actual result and deduce how many numbers had been added together, because 10, 20, 100 zeros all sum to the same amount.

This evening, I tried a different initial test:

The results are much better - fence post mistakes change the observable behavior in this circumstance, and are therefore easy to catch. The deviations from the expected results give an immediate hint at the error. We know from taking small steps which edit introduced a fault, but the distinct behaviors mean that it is easy to recognize the precise nature of the fault.

In this evenings ending, I managed to get all the way to make the next change easy: using the gutter game as my second test produced a trivial pass, because the faults I introduced during refactoring had already been detected and mitigated.

TDD: On Fake Code

This past spring, David Tanzer published a short essay on transitioning from fake implementations to real ones.

When you do TDD, “fake implementations” or “wrong code” are OK, as long as they pass all the tests you have so far
But when do you stop to fake? When do you start writing “real code”?

Tanzer is using this as a stepping stone to introduce Uncle Bob's heuristic: as the tests get more specific, the code gets more generic.

But there is another answer, which I eventually learned from a comment written by Kent Beck:

Do you have some refactoring to do first?

Here is Tanzer's passing implementation:
And that's fine for our test calibration; we have successfully demonstrated that the test can distinguish the correct behavior from an incorrect behaviod in this specific case.

But... the current implementation implicitly describes two pieces of domain knowledge that we can make explicit.

• The length of the hint should be the same as the length of the secret word.
• The initial representation of the hint should conceal all of the letters in the secret word, which is to say it should be entirely composed of the unrevealed letter token "_".

We don't have to wait for permission to introduce these ideas; they are always going to appear in a refactoring step, so we can cut to the chase and introduce them immediately.

From there, we might notice that the secretWord we are using in the hint method is the same that was passed to the constructor, and extract that duplication. Or we might decide that the creation of the hint of the correct length is a single idea that can be extracted into another function, and do that.

You can start writing the real code as soon as you have a green bar.

Because I was reviewing Saff and Boshernitsan today, I have been thinking about Beck's Money demonstration.  Translated into Python, Beck's first test looks like

Riddle: what's the simplest implementation that will pass this test? There are probably several different answers, but the simplest I can come up with looks like:

No implementation, no variable names. Just 10. It's clear to me that this is "wrong code", in Tanzer's sense. But we don't need more tests to make it better, we can immediately refactor (in Beck's sense) to restore sanity to the implementation.

If we were being very small and deliberate in our refactoring, the refactoring sequence might look like:
Like "triangulation", small and deliberate steps are not required - they are a technique to practice so that you can get small when larger steps aren't working.

Thoughts on an Acceptance Tests

In my recent experiments with Hunt the Wumpus, I started thinking about what an "acceptance" test might look like.

To get started, I reviewed the walking skeleton example in Growing Object Oriented Software.  Freeman and Pryce wrote that the initial iteration should include delivery of a completely automated checkout/build/deploy/test pipeline, front loading the work of solving a number of critical system and political issues.  The acceptance test, in their example, launches the application and uses the user interface to probe and measure the app.

For an interactive shell app like Wumpus, the test harness is relatively straight forward; we control stdin to pass data to the app and control stdout to read data from the app.

What I struggle with, at this point in the narrative, is the amount of work required to create stable acceptance tests.

A point of view: automated checks are mistake detectors.  They don't provide value to the user - you can delete all of your automated checks and the behavior of your production code doesn't change.  Economically, the justification for the tests is that they reduce the costs of future work.  More precisely, we adopt processes that shutdown when a mistake is detected, ensuring that the mistakes cannot be overlooked, and that we don't expose our test subjects to expensive evaluation when the more cost effective checks have already detected problems.

There's another potential benefit to checks, which the TDD ritual seeks to exploit: thinking about how the checks will validate the behavior of your application creates space to discover important ideas in your app before you start coding it.




The acceptance tests, what with all the work we need to do to set them up, are expensive relative to other mechanisms for checking the correctness of the program.  In the case of the Auction Sniper, those tests included measuring that the app could talk to other processes.

In the case of Wumpus, there really aren't other processes to talk to unless we choose a particularly contrived design.  Only the interface to the user is interesting.  So there isn't a lot of complexity that
needs to be evaluated from the outside.

Which is good, because that evaluation is painful.

Wumpus has three awkward aspects to it; hidden information, non-deterministic behavior, and message schema.

The hidden information aspect is what introduces uncertainty in the game - with complete knowledge of the hazards in the maze, the game can be won trivially by shooting the wumpus in its lair.  But without that hidden information, one cannot know the correct outcome of any action by the hunter.


The location of the hazards in the game is non-deterministic - that's part of the mechanism for hiding that information from the player.  In addition, each of the hunters actions can induce random behavior by the hazards in the game.  These random effects mean that any given action by the player can have multiple candidate responses, depending on how the dice fall.

The feedback from the game to the player is all via messages written to the console.  Those messages were designed (such as it is) for human readability, rather than machine readability.  Understanding the semantics of those messages requires introducing a parser into the acceptance test.

What this means is that we have some work cut out for us if we want anything more than a trivial verification that some message was written to standard out.

One possibility is that we can introduce the idea of specifying a seed for the non-deterministic behavior from outside the program.  The acceptance test can fix the seed, then perform a domain agnostic comparison of the output to some golden master that we specify.  This is somewhat brittle: the current mapping of random values to representations is arbitrary, and the domain agnostic match over fits the representation of the messages.

Another possibility is to introduce an affordance that allows the specification of a message schema to use; the acceptance test simply switches the application into a mode where the responses are easy to parse, much like an http request might distinguish between text/plain and application/json.  Even without fixing the seed, our acceptance test can still easily identify that all of the messages are well formed.

The schema approach, while straight forward, feels like a lot of work that will not pay off.  I think the issue here is that, while wumpus is a more interesting toy exercise than the bowling game or a Fibonacci calculator, it is still fundamentally a toy problem -- one with an arbitrary and limited scope.

My null-design port of Wumpus from basic to Java is only 375 lines long; it's hard to envision that project having a lifetime that justifies heavy upfront investment in acceptance tests.

What we can do, from the outset, is decide that the behaviors that the acceptance test needs to control - the random seed, the interpretation of the random values, the message schema - can be controlled from the outside, and that the idiom for changing those behaviors in the future is to extend the application with new selectable behaviors, rather than replacing the existing behaviors.

Purchase Approval

One problem I've had with Domain Driven Design is coming up with good realistic examples that exhibit the sorts of complexity we need to be thinking about, without getting lost in the weeds.

My latest idea is to try working through a purchase approval in an analog office.

Bob wants the company to pay for something.  So he gets a blank form, and fills in the details, and drops off the form with Alice.  Alice does the work of comparing the details to the current policies, and approving / rejecting the request.  The resolved request is returned to Bob, so that he can act on the decision that has been made.

There are a lot of requests, and checking the details is a lot of work.  So Alice has become a bottleneck.  She offloads some of the work to Terry the intern; Terry does the legwork for requests when the approval doesn't require Alice's domain expertise.

As a proxy for easy, we'll use a trivial condition like "amount less than 100 USD".

The form acts as a sort of lock; an actor in this protocol can only change the paper when they have physical control of it.  So the process is serial, only one person can record information at a time.

That means we need to think more precisely about how the requests are shared by Alice and Terry.  Perhaps all requests go first to Alice, and she passes the easy requests to Terry; or perhaps the requests all go to Terry, and the hard cases are forwarded to Alice.

We can think of the request as a single form, that gets modified.  Alternatively, we can think of an envelope filled with "immutable" documents; each actor adds new paperwork to the envelope.

The process is asynchronous, in this sense - the request can be in Alice's office even though Alice herself is out at lunch, or home sick.  The movement of paper allows the people to communicate, even though they aren't necessarily in the office at the same time.

The paperwork is anemic - all of the domain knowledge is locked in the heads of Alice and Terry (and, to some degree, Bob).  The paperwork is just the bookkeeping.

It's also worth noting that the paper is immutable, in this sense: once the paperwork has left Bob's control, he cannot correct errors until the paperwork is returned to him.

Bob's "view" of this process is the stack of blank forms, and his collection of resolved requests.  Alice and Terry have similar views: stacks of pending requests.

Exercise 1: what changes when we take this process digital?  So instead of physical paperwork moving from place to place, we now have information being copied from one place to another.

Exercise 2: what changes when we extend the digital process to automate Terry's work?

TDD: Random is Arbitrary

I happened across a Yahtzee kata today. Although I didn't work that exercise today, it got me thinking again about random behaviors.

Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin.

If your goal is to write fast, deterministic tests that you can use to detect unintended changes during a refactoring, then you need to treat a random number generator the way you would a clock.  The test itself has to decide which random sequence to provide, and pass it to the test subject.

But there's a second problem, which is this -- if a random choice from a list is an acceptable behavior, then so to must be the same random choice from every permutation of that list.

If we can map a sequence of random numbers to [HEADS, TAILS], and produce from that an acceptable behavior, then it must also be true that mapping the same sequence of random numbers to [TAILS, HEADS] must also be acceptable.  You can replace one with the other any time you want.

But doing that isn't a refactoring; when we make this change, the same inputs produce different outputs, which are measured by the test harness.

The choice of which permutation to use is an implementation detail; any tests that depend on the specific requirements are overfit.

Can you beat this by passing in an ordered list of choices?  Not really, for the same reason - if the permutation of items that you pass in produces an acceptable behavior, then it sill also be acceptable for the code under test to re-order those items before using them.

Anoher related problem is that there are different ways to interact with the random number generator that produce equally acceptable results.  If we want to randomly toss three coins, we can pull three random numbers and project each onto [0,1], and encode the result, or we can pull a single random number, project onto [0,7], and then use a squashed encoding to interpret the result.  If one is valid, then so to is the other -- but they leave the RNG in different states, and therefore we have additional risks of overfitting.

What does this mean?  That simply decoupling the random number generator isn't enough.  We need to be passing the result of the random choice - pass in the coin after it has been flipped, pass in the dice after they have been rolled, pass in the deck after it has been shuffled.

It's not enough to inject the random number generator into the test; you need to leave the arbitrary mapping of the random number to some result value in the imperative shell as well.