Where unit testing fails

http://www.hmemcpy.com/blog/2011/06/where-unit-testing-fails/?utm_source=hacker-news&utm_medium=social-media&utm_campaign=typemock-where-ut-fails

by fafssaf • 15 years ago

65 50 15 years ago

hmemcpy.com

perlgeek• 15 years ago

Ok, TDD didn't help with designing an algorithm for Lychrel number - because you just don't get around implementing the loop that tests if a number is a lychrel number, and it's very simple.

But to me that's not the whole purpose of unit tests - the most important part for me is that it tells you very quickly when you have bugs in your implementation. Somehow the author neglects to address this very central point.

Luyt• 15 years ago

The exact Sudoku URLs mentioned in the article, just checked/updated:

Ravi's article: http://ravimohan.blogspot.com/2007/04/learning-from-sudoku-s...

Peter Norvig's solver: http://norvig.com/sudoku.html

Ron Jeffries' attempts:

http://xprogramming.com/articles/sudokumusings/

http://xprogramming.com/articles/oksudoku/

http://xprogramming.com/articles/sudoku2

http://xprogramming.com/articles/sudoku4

http://xprogramming.com/articles/sudoku5

And, as dessert (Ron is very frank about his failures):

http://xprogramming.com/articles/roroncemore/

"This is surely the most ignominious debacle of a project listed on my site, even though others have also not shipped. (Sudoku did not ship and will not. Shotgun will go forward if the Customer wants to.)"

peteretep6• 15 years ago

Whut?

Listen kids, testing is a tool for HELPING THE DEVELOPER, not for using to engage in a "more pious than thou" dick-swinging my Cucumber is bigger than yours idiocy.

Testing is about giving YOU THE DEVELOPER useful and quick feedback about if you're on the right path, and if you've broken something, and for warning people who come after you if they've broken something. It's not an arcane methodology that somehow has some magical "making your code better" side-effect...

The whole concept of "test driven development" is hocus, and I speak this as someone who writes a lot of tests, and who charges a lot of money for fixing test suites. Instead: developer-driven testing. Give your developers useful tools for solving problems and supporting themselves, rather than disappearing in to some testing hell where you're doing it a certain way because you're supposed to.

Volpe3• 15 years ago

> The whole concept "test driven development" is hocus...

I've worked on numerous projects where TDD has (and continues) to prove invaluable.

So regardless how much experience you've got, I've had experience to the contrary, thus the "whole concept" isn't hocus.

Why have you come to believe this?

peteretep6• 15 years ago

It's hocus where contrasted to developer-driven testing, because Test Driven Development - as a development methodology (as opposed to a tool) - espouses that you Write All Your Tests first.

Have I had experience (and much value) out of sometimes writing tests for certain problem classes before writing any code? Yes. Changes to existing functionality are often a good candidate.

Does TDD as a methodology suggest you should ALWAYS write your tests first? Everything I've read suggests so.

And "as any fule kno" [sic], this is idioicy during a design or hacking or greenfield phase of development. Allowing your tests to dictate your code (rather than influence the design of modular code) and to dictate your design because you wrote over-invasive test.

tl;dr: Writing tests before code works pretty well in some situations. Test Driven Development, as handed down to us mortals by Agile Testing Experts and other assorted shills, is hocus.

smackay• 15 years ago

The issue/argument here is not that writing tests is worthless but that in many cases the approach of "if we write enough tests then the code that solves the problem will eventually emerge" is doomed to failure or at least results in an extremely verbose approach to development.

jdlshore• 15 years ago

I'm seeing a lot of misconceptions about test-driven development in this thread. The biggest one is that test-driven development involves writing a bunch of tests first. Instead, TDD involves interweaving tests and production code in a very tight cycle. You write a few lines of test code, then a few lines of production code, then you review and improve your code, then write a few lines of test code, and so forth. Each step only takes a minute or so.

This is useful because you're constantly making and checking hypotheses: "This code should make a test fail in X way... yup. Okay, now this code should make the test pass. Yup. Now this change shouldn't change behavior, and the tests should still pass. Oops! Undo. Oh, that method has to be called in the constructor. All right, this change should work. Good."

(If you're interested, my book goes into more detail, and it's online: http://jamesshore.com/Agile-Book/test_driven_development.htm... . I also have a extensive screencast of real-world TDD here: http://jamesshore.com/Blog/Lets-Play/ )

Despite the extremists, TDD really is a useful tool--and that's all it is. Sure, TDD has been turned into yet another vehicle for programmers to engage in religious wars, but you can't really blame TDD for that, any more than you can blame Richard Stallman for emacs vs. vi wars.

nickik• 15 years ago

First write the high level test. Then start implmenting and when you writte a helper function, write a little test for that function too.

Don't just write all the test for every little function in the beginning thats stupid, How do you even know what helper function you need to implment.

latch2• 15 years ago

There are a couple tricks to effective unit testing. Ultimately though, the goal is to write non-brittle tests. That is, tests that won't break due to unrelated changes. Get this wrong and the cost of maintaining your tests will outweigh the benefits.

Achieving this, in my experience, comes down to disciplined used of mocks and stubs. I've seen people lean too heavily on them, or not heavily enough. The biggest problem I've seen, particularly common in the Java world due to jMock's datedness, is over specifying expectations on mocks. Stubs which can provide canned responses (whether through a framework or manually rolled) are absolutely and totally the most underused yet useful tool in your testing arsenal.

jsdalton3• 15 years ago

Can you expand a bit on the distinction you're making between mocks and stubs, and why you believe stubs are both underused and useful?

Perhaps I'm doing it wrong, but I've found in my experience that bugs I miss in testing increase proportionally with my use of mocks or stubs. Invariably, when I'm forced to stub something and replicate its behavior I miss something subtle that comes back to bite me.

latch2• 15 years ago

I think there's 2 problem.

First, people rely too heavily on mocks/stubs/fakes/(whatever you want to call them). This has gotten better in the past 4 or so years (in my mind, largely because of Rails and it being "acceptable" to hit a DB in a test - though it might actually predate Rails). I think this problem is pretty straightforward to understand (again, especially when you look at the Rails way to test a DB interaction versus a more "traditional" way).

However, there are instances where mocks/fakes/stubs are important. Some outside dependencies might not be accessible during testing, might not be predictable/deterministic, might be too slow or might simply involve too much setup. Also, solely relying on "real" implementations can also make your tests too brittle. Why should the logic for can_legally_drink? break if the DB column is changed from DOB to dateofbirth (ok, that's an extreme and poor example, but you get the idea, hopefully).

Anyways, assuming you agree that sometimes a fake is simply better, you get into mocks vs stubs. To me a stub is dumb and a mock is strict. Stubs also automatically reply with canned answers, mocks don't. A mock is used to assert that a certain expected call was made. A stub is used just to get your test to move over a line of code.

The problem is that people use mocks over and over again. Re-specifying the same expectations in every test..making X tests break when you change the behavior of the interaction, versus just 1 test. As semi-pseudocode (and yes, it might be better to just hit the DB in this case):

  def self.login_user(name, password)
    user = Store.get_user_by_name(name)
    return user.nil? || user.password != password ? nil : user
  end

To me, you kinda wanna check that the above code properly interacts with someStore. This is when you use a mock:

  it "gets the user from the store" do
    Store.should_receive(:get_user_by_name).with('leto')
    User.login_user ('leto', 'ghanima')
  end

You also want to make sure the password matching works. This is where people go wrong. They'll use a mock (strict) again..which'll just repeat the above code...except this test has really nothing to do with how store...we just want to get over the line of code:

  it "returns nil if the passwords don't match" do
    Store.stub!(:get_user_by_name).and_return(User.new)
    User.login_user('leto', 'ghanima').should be_nil
  end

If you are familiar with jMock, it's kinda the difference between allowing and oneOf. oneOf is very strict, allowing isn't. You really should use allowing whenever you aren't explicitly testing the interaction (and you shouldn't explicitly test the interaction in more than 1 test (dedicated to testing said interaction)).

Some framework even return smart canned answers. So instead of returning nil, they'll default to a new instance of the type, or an empty array, or some default scalar value (like an empty string). This is particularly useful when you just want to get passed a null reference (which is exceedingly common).

Does that make sense?

chrislloyd• 15 years ago

I can't help but appreciate the irony of a link titled "Where unit testing fails" leading to a WordPress database connection error.

hmemcpy2• 15 years ago

Sorry, my hosting is probably not... used to any traffic :) Should be ok now...

rimantas• 15 years ago

So you think unit tests would help with that?

lhnz• 15 years ago

That's the point. Most unit tests wouldn't stop this kind of problem. ;)

hmemcpy2• 15 years ago

Sorry for the late reply.

That's an interesting question - would a unit test prevent this error? To answer this, let's consider what happened: the database didn't respond in an appropriate way, and probably returned an error. I'm not exactly sure what exact error was displayed, but WordPress has caught this situation, and handled it the best it could - displaying a proper error. I would write a unit test for this exact scenario - using a fake (mock) object, simulate the database timeout, and make sure that the error was caught and handled appropriately. Other then that there's no real other way to gracefully recover.

augustl• 15 years ago

I like to think of it this way:

When writing code it is imperative to to get great feedback, as often as possible. In a number of cases, TDD helps you do that. In cases where it don't, well, it doesn't, so don't use it.

fafssaf• 15 years ago

What are some cases that you would and wouldn't use unit tests? Igal is doing a webinar https://www2.gotomeeting.com/register/545851563

paganel• 15 years ago

Maybe I'm in a mad mood or somth (it's Monday, after all) but all this "let's write a parallel world, called TDD, to which the actual production code has to comply and praise and give sacrifices"-mantra has gotten a little over the top.

Don't get me wrong, I'm sure that all these guys and chicks that live and die by TDD are smart (probably smarter than me), but what they are building is starting to get more and more out of touch with real-world requirements (I wanted to say somth about how this resembles a schizophrenic world, but for the moment I'll stop short of that).

My father was a civil engineer, at a time when they didn't have AutoCAD available and all that fancy computer stuff. As he elegantly put it: "if I mess things up in my work people will die, either in 2 weeks or in 20 years, when the next big earthquake will hit us". Well, I never saw him "testing" building apartment-blocks, or industrial buildings, or roads, he made sure that what was on the sheet of papers where the construction plans were drawn would get built as accurate as possible in real life. And keep in mind that he was managing construction workers, many of them close to illiterate, even former convicts, and not CS-graduates. That's the job of all civil engineers from all over the world. So, if they can do it, why in the name of God do we programmers write tests for mundane stuff like sudoku-solvers? Something is not right.

peteretep6• 15 years ago

Civil Engineers these days (or this is my understanding, anyway) DO use AutoCAD and 'all the fancy computer stuff' because testing allows you to code more productively, when you do it right. That's why engineers these days do automated simulations...

At the point where you're writing tests to impress other programmers (see article) about how much of a 'craftsman' you are, you lose. When you're writing tests that help you as a developer, and help get the software out more quickly and with higher quality, then you're doing it right.

kenjackson• 15 years ago

TDD is new abstract concrete factory of super factories. People who get so caught up in an ideal, they lose focus of actually delivering solutions.

wnight3• 15 years ago

Surely he did though. At some point he (roughly) had to add up the weight of the building and make sure the supports were thick enough to bear it. It's just too basic to talk about.

colin_jack• 15 years ago

I haven't had time to read them all yet so I was wondering if someone could give me a summary of why the TDD based sudoku approach failed?

eru2• 15 years ago

The guys approach to the problem wasn't smart enough.

Testing doesn't help you come up with good algorithms. It can help you with not messing up an implementation, though.

damoncali• 15 years ago

Here's my trouble with testing as espoused by proponents of TDD: I bought into the Agile Manifesto. I believe in working code over specifications. How then, am I supposed to write a bunch of tests that will in turn tell me what code to write?

It is not a coincidence that one of the reasons TDD'ers love rspec so much is that the "code reads like documentation" - it's even called r spec.

Perhaps that is ok for mature projects. But I often hear TDD and agile used together as if they weren't in conflict and I get confused. Then again, I've only ever worked on new projects.

Maybe I'm missing something?

Where unit testing fails

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