In web development there is a lot of focus on REST-style architectures, with the objectives of minimizing (or eliminating) state. The web frameworks that I have seen all emphasize this style (Django, Rails, flask, etc.).
While I agree that this is a good fit for the web in general, there are also many cases where this is inadequate. In particular I am thinking of the case where you want the user to follow a process, i.e. you want to offer a number of steps and these steps should be completed in a certain order (possibly with optional steps, deviating paths, etc.)
A good example of this might be a shopping cart: First you have to make your selection, then enter your address, choose shipment type, enter your payment details, finish. You don't want the user to skip any of these steps and the process can become a lot more complex. Ideally I would want this process to be defined in a separate place to separate this logic from the rest of the implementation.
Now my questions:
Are finite state machines the way to go here? Do they still work well if these processes become complex and need to change a lot (e.g. this step should go here, this step should go into this process instead, etc)?
What options are offered by/for web frameworks (not any in particular I am interested in the best solutions)?
What are interesting / good examples of where such processes occur? Shopping carts are an obvious example but I am sure there are lots more.
Yes, they are. Using state machines (workflows) is an appropriate solution for the problem you described. If designed well it can make your code more cleaner, remove mess from the code. Logic of each state and transition logic are incapsulated within a State class object so the code looks cleaner and more maintainable . Implementations may vary (say, the place you keep your transition logic - within state or create a separate transition manager) and don't match canonical description of state machine in discrete math so you'd better try what works for you better.
For Ruby you can check workflow: https://github.com/geekq/workflow or stonepath: https://github.com/bokmann/stonepath. State machine pattern is also can be found in javascript frameworks (SpoutCore). It's not difficult to implement your own small state machine engine.
Interesting examples? Lots of them. Processing orders, banking operations, games. I used state machine when created behaviour correction module which includes phychological tests, games, video. The transitions from state to state depended there on if tests are answered correctly, if game played successfully etc.
PS. I used the terms of state machine and workflow as synonyms but they are not the same; it was discussed here: http://jmettraux.wordpress.com/2009/07/03/state-machine-workflow-engine/ . You can also find some Ruby code and links there.
I want to take a BDD approach to unit testing in an iOS project, and I just realized that there may not be an existing library that provides test doubles of the test spy variety. Ideally, I'm looking for something similar to Mockito, Jasmine, or RR.
Before I go and spend a week of free time writing a test spy library, I thought I'd pose the question here on SO first.
So far I've looked at OCMock and Kiwi, but they both seem to be of the traditional high-specification-by-default mocking frameworks that require expectation assertions be set in the arrange phase, prior to the act phase. Obviously, this is hampering my vision of beautiful, DRY, nested specs (which I plan on authoring in either Kiwi or Cedar).
Just saw this.
Kiwi definitely does not do this now. You are right that the mocks in it are built for a 'standard' arrange prior to act phase.
Moving on, albeit at first glance, it seems that adding the basics for spy functionality would not require too much reengineering. Every message (barring some implementation important, reserved selectors) that gets to a mock goes through -[KWMock forwardInvocation:].
Essentially, the current -[KWMock forwardInvocation:] would need be modified to record/copy all invocations that pass through it, instead of what it does now. This would be the primitive functionality that would allow expectations to be verified later by querying the recorded invocations. Of course, coming up with a nice readable form for verification isn't trivial either.
The spy/mock would still need to know what class/protocol it is standing in for upfront. This is so it will be able to generate valid method signatures for selectors of messages sent to it that allows the runtime forwarding machinery to generate the actual NSInvocation that will be forwarded.
I am preoccupied with other things right now to get an implementation in there, but I'll be happy to answer more questions or merge any pull requests. HTH.
These I come across this term a lot "crosscutting requirements/concerns" in programming world.
Although I think I have an idea what it means still I do not have a clear idea. I hear it a lot in web service and SOA in general.
Can this be explained using a hello world example?
It tends to mean "stuff that you want to do in lots of places, which doesn't have an awful lot to do with the real meat of that piece of code".
Common examples are:
Transaction handling
Security
Logging
Error handling
I find it's usually mentioned in respect to Aspect-Oriented Programming (AOP) which usually attempts to handle things like this declaratively, e.g. with attributes/annotations. As a gross simplification, it's a case of applying boiler-plate code (e.g. to verify the identity/authority of the user in the current context, or to log entry/exit of the method) automatically without making the code itself messy.
The standard "hello world" example for crosscutting is logging: You have an error in your production system and you have no clue what is going on. To solve it, you really need to see which functions in your code are called and what parameters they get and what they return.
This is a simple task that can be fully automated: Locate all functions (or a subset using a filter of some kind) and add a logging call to them which prints the name and the parameters. Since the code contains all the information you need to complete this task, what you really want is a tool that does it for you and which does it in a single place (instead of having you edit thousands of source files adding log statements everywhere).
I recommend you look at a framework like Postsharp and try out this example from the postsharp site. If you know java a lok into AspectJ is worth a look. But first you may want to read the link posted by Jon Skeet :)
I'm occasionally unfortunate enough to have to make alterations to very old, poorly not documented and poorly not designed code.
It often takes a long time to make a simple change because there is not much structure to the existing code and I really have to read a lot of code before I have a feel for where things would be.
What I think would help a lot in cases like this is a tool that would allow one to visualise an overview of the code, and then maybe even drill down for more detail. I suspect such a tool would be very hard to get right, given that is trying to find structure where there is little or none.
I guess this is not really a question, but rather a musing. I should make it into a question - What do others do to assist in getting their head around other peoples code, the good and the bad?
Hmm, this is a hard one, so much to say so little time ...
1) If you can run the code it makes life soooo much easier, breakpoints (especially conditional) break points are you friend.
2) A purists' approach would be to write a few unit tests, for known functionality, then refactor to improve code and understanding, then re-test. If things break, then create more unit tests - repeat until bored/old/moved to new project
3) ReSharper is good at showing where things are being used, what's calling a method for instance, it's static but a good start, and it helps with refactoring.
4) Many .net events are coded as public, and events can be a pain to debug at the best of times. Recode them to be private and use a property with add/remove. You can then use break point to see what is listening on an event.
BTW - I'm playing in the .Net space, and would love a tool to help do this kind of stuff, like Joel does anyone out there know of a good dynamic code reviewing tool?
I have been asked to take ownership of some NASTY code in the past - both work and "play".
Most of the amateurs I took over code for had just sort of evolved the code to do what they needed over several iterations. It was always a giant incestuous mess of library A calling B, calling back into A, calling C, calling B, etc. A lot of the time they'd use threads and not a critical section was to be seen.
I found the best/only way to get a handle on the code was start at the OS entry point [main()] and build my own call stack diagram showing the call tree. You don't really need to build a full tree at the outset. Just trace through the section(s) you're working on at each stage and you'll get a good enough handle on things to be able to run with it.
To top it all off, use the biggest slice of dead tree you can find and a pen. Laying it all out in front of you so you don't have to jump back and forward on screens or pages makes life so much simpler.
EDIT: There's a lot of talk about coding standards... they will just make poor code look consistent with good code (and usually be harder to spot). Coding standards don't always make maintaining code easier.
I do this on a regular basis. And have developed some tools and tricks.
Try to get a general overview (object diagram or other).
Document your findings.
Test your assumptions (especially for vague code).
The problem with this is that on most companies you are appreciated by result. That's why some programmers write poor code fast and move on to a different project. So you are left with the garbage, and your boss compares your sluggish progress with the quick and dirtu guy. (Luckily my current employer is different).
I generally use UML sequence diagrams of various key ways that the component is used. I don't know of any tools that can generate them automatically, but many UML tools such as BoUML and EA Sparx can create classes/operations from source code which saves some typing.
The definitive text on this situation is Michael Feathers' Working Effectively with Legacy Code. As S. Lott says get some unit tests in to establish behaviour of the lagacy code. Once you have those in you can begin to refactor. There seems to be a sample chapter available on the Object Mentor website.
I strongly recommend BOUML. It's a free UML modelling tool, which:
is extremely fast (fastest UML tool ever created, check out benchmarks),
has rock solid C++ import support,
has great SVG export support, which is important, because viewing large graphs in vector format, which scales fast in e.g. Firefox, is very convenient (you can quickly switch between "birds eye" view and class detail view),
is full featured, intensively developed (look at development history, it's hard to believe that so fast progress is possible).
So: import your code into BOUML and view it there, or export to SVG and view it in Firefox.
See Unit Testing Legacy ASP.NET Webforms Applications for advice on getting a grip on legacy apps via unit testing.
There are many similar questions and answers. Here's the search https://stackoverflow.com/search?q=unit+test+legacy
The point is that getting your head around legacy is probably easiest if you are writing unit tests for that legacy.
I haven't had great luck with tools to automate the review of poorly documented/executed code, cause a confusing/badly designed program generally translates to a less than useful model. It's not exciting or immediately rewarding, but I've had the best results with picking a spot and following the program execution line by line, documenting and adding comments as I go, and refactoring where applicable.
a good IDE (EMACS or Eclipse) could help in many cases. Also on a UNIX-platform, there are some tools for crossreferencing (etags, ctags) or checking (lint) or gcc with many many warning options turned on.
First, before trying to comprehend a function/method, i would refactor it a bit to fit your coding conventions (spaces, braces, indentation) and remove most of the comments if they seem to be wrong.
Then I would refactor and comment the parts you understood, and try to find/grep those parts over the whole source tree and refactor them there also.
Over the time, you get a nicer code, you like to work with.
I personally do a lot of drawing of diagrams, and figuring out the bones of the structure.
The fad de jour (and possibly quite rightly) has got me writing unit tests to test my assertions, and build up a safety net for changes I make to the system.
Once I get to a point where I'm comfortable enought knowing what the system does, I'll take a stab at fixing bugs in the sanest way possible, and hope my safety nets neared completion.
That's just me, however. ;)
i have actuaally been using the refactoring features of ReSharper to help m get a handle on a bunch of projects that i inherited recently. So, to figure out another programmer's very poorly structured, undocumented code, i actually start by refactoring it.
Cleaning up the code, renaming methods, classes and namespaces properly, extracting methods are all structural changes that can shed light on what a piece of code is supposed to do. It might sound counterintuitive to refactor code that you don't "know" but trut me, ReSharper really allows you to do this. Take for example the issue of red herring dead code. You see a method in a class or perhaps a strangely named variable. You can start by trying to lookup usages or, ungh, do a text search, but ReSharper will actually detect dead code and color it gray. As soon as you open a file you see in gray and with scroll bar flags what would have in the past been confusing red herrings.
There are dozens of other tricks and probably a number of other tools that can do similar things but i am a ReSharper junky.
Cheers.
Get to know the software intimately from a user's point of view. A lot can be learnt about the underlying structure by studying and interacting with the user interface(s).
Printouts
Whiteboards
Lots of notepaper
Lots of Starbucks
Being able to scribble all over the poor thing is the most useful method for me. Usually I turn up a lot of "huh, that's funny..." while trying to make basic code structure diagrams that turns out to be more useful than the diagrams themselves in the end. Automated tools are probably more helpful than I give them credit for, but the value of finding those funny bits exceeds the value of rapidly generated diagrams for me.
For diagrams, I look for mostly where the data is going. Where does it come in, where does it end up, and what does it go through on the way. Generally what happens to the data seems to give a good impression of the overall layout, and some bones to come back to if I'm rewriting.
When I'm working on legacy code, I don't attempt to understand the entire system. That would result in complexity overload and subsequent brain explosion.
Rather, I take one single feature of the system and try to understand completely how it works, from end to end. I will generally debug into the code, starting from the point in the UI code where I can find the specific functionality (since this is usually the only thing I'll be able to find at first). Then I will perform some action in the GUI, and drill down in the code all the way down into the database and then back up. This usually results in a complete understanding of at least one feature of the system, and sometimes gives insight into other parts of the system as well.
Once I understand what functions are being called and what stored procedures, tables, and views are involved, I then do a search through the code to find out what other parts of the application rely on these same functions/procs. This is how I find out if a change I'm going to make will break anything else in the system.
It can also sometimes be useful to attempt to make diagrams of the database and/or code structure, but sometimes it's just so bad or so insanely complex that it's better to ignore the system as a whole and just focus on the part that you need to change.
My big problem is that I (currently) have very large systems to understand in a fairly short space of time (I pity contract developers on this point) and don't have a lot of experience doing this (having previously been fortunate enough to be the one designing from the ground up.)
One method I use is to try to understand the meaning of the naming of variables, methods, classes, etc. This is useful because it (hopefully increasingly) embeds a high-level view of a train of thought from an atomic level.
I say this because typically developers will name their elements (with what they believe are) meaningfully and providing insight into their intended function. This is flawed, admittedly, if the developer has a defective understanding of their program, the terminology or (often the case, imho) is trying to sound clever. How many developers have seen keywords or class names and only then looked up the term in the dictionary, for the first time?
It's all about the standards and coding rules your company is using.
if everyone codes in different style, then it's hard to maintain other programmer code and etc, if you decide what standard you'll use have some rules, everything will be fine :) Note: that you don't have to make a lot of rules, because people should have possibility to code in style they like, otherwise you can be very surprised.
Mock frameworks, e.g. EasyMock, make it easier to plugin dummy dependencies. Having said that, using them for ensuring how different methods on particular components are called (and in what order) seems bad to me. It exposes the behaviour to test class, which makes it harder to maintain production code. And I really don't see the benefit; mentally I feel like I've been chained to a heavy ball.
I much rather like to just test against interface, giving test data as input and asserting the result. Better yet, to use some testing tool that generates test data automatically for verifying given property. e.g. adding one element to a list, and removing it immediately yields the same list.
In our workplace, we use Hudson which gives testing coverage. Unfortunately it makes it easy to get blindly obsessed that everything is tested. I strongly feel that one shouldn't test everything if one wants to be productive also in maintenance mode. One good example would be controllers in web frameworks. As generally they should contain very little logic, testing with mock framework that controller calls such and such method in particular order is nonsensical in my honest opinion.
Dear SOers, what are your opinions on this?
I read 2 questions:
What is your opinion on testing that particular methods on components are called in a particular order?
I've fallen foul of this in the past. We use a lot more "stubbing" and a lot less "mocking" these days.
We try to write unit tests which test only one thing. When we do this it's normally possible to write a very simple test which stubs out
interactions with most other components. And we very rarely assert ordering. This helps to make the tests less brittle.
Tests which test only one thing are easier to understand and maintain.
Also, if you find yourself having to write lots of expectations for interactions with lots of components there could well be a problem in the code you're testing anyway. If it's difficult to maintain tests the code you're testing can often be refactored.
Should one be obsessed with test coverage?
When writing unit tests for a given class I'm pretty obsessed with test coverage. It makes it really easy to spot important bits of behaviour that I haven't tested. I can also make a judgement call about which bits I don't need to cover.
Overall unit test coverage stats? Not particularly interested so long as they're high.
100% unit test coverage for an entire system? Not interested at all.
I agree - I'm in favor of leaning heavily towards state verification rather than behavior verification (a loose interpretation of classical TDD while still using test doubles).
The book The Art of Unit Testing has plenty of good advice in these areas.
100% test coverage, GUI testing, testing getters/setters or other no-logic code, etc. seem unlikely to provide good ROI. TDD will provide high test coverage in any case. Test what might break.
It depends on how you model the domain(s) of your program.
If you model the domains in terms of data stored in data structures and methods that read data from one data structure and store derived data in another data structure (procedures or functions depending how procedural or functional your design is), then mock objects are not appropriate. So called "state-based" testing is what you want. The outcome you care about is that a procedure puts the right data in the right variables and what it calls to make that happen is just an implementation detail.
If you model the domains in terms of message-passing communication protocols by which objects collaborate, then the protocols are what you care about and what data the objects store to coordinate their behaviour in the protocols in which they play roles is just implementation detail. In that case, mock objects are the right tool for the job and state based testing ties the tests too closely to unimportant implementation details.
And in most object-oriented programs there is a mix of styles. Some code will be written purely functional, transforming immutable data structures. Other code will be coordinating the behaviour of objects that change their hidden, internal state over time.
As for high test coverage, it really doesn't tell you that much. Low test coverage shows you where you have inadequate testing, but high test coverage doesn't show you that the code is adequately tested. Tests can, for example, run through code paths and so increase the coverage stats but not actually make any assertions about what those code paths did. Also, what really matters is how different parts of the program behave in combination, which unit test coverage won't tell you. If you want to verify that your tests really are testing your system's behaviour adequately you could use a Mutation Testing tool. It's a slow process, so it's something you'd run in a nightly build rather than on every check-in.
I'd asked a similar question How Much Unit Testing is a Good Thing, which might help give an idea of the variety of levels of testing people feel are appropriate.
What is the probability that during your code's maintenance some junior employee will break the part of code that runs "controller calls such and such method in particular order"?
What is the cost to your organization if such a thing occurs - in production outage, debugging/fixing/re-testing/re-release, legal/financial risk, reputation risk, etc...?
Now, multiply #1 and #2 and check whether your reluctance to achieve a reasonable amount of test coverage is worth the risk.
Sometimes, it will not be (this is why in testing there's a concept of a point of diminishing returns).
E.g. if you maintain a web app that is not production critical and has 100 users who have a workaround if the app is broken (and/or can do easy and immediate rollback), then spending 3 months doing full testing coverage of that app is probably non-sensical.
If you work on an app where a minor bug can have multi-million-dollar or worse consequences (think space shuttle software, or guidance system for a cruise missile), then the thorough testing with complete coverage becomes a lot more sensical.
Also, i'm not sure if i'm reading too much into your question but you seem to be implying that having mocking-enabled unit testing somehow excluds application/integration functional testing. If that is the case, you are right to object to such a notion - the two testing approaches must co-exist.