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I am yet to jump into the TDD/BDD group. Trying to make the mental switch. For now I have been writing the business logic before my tests.
In one of my Rails model, I have a complex algorithm implemented. The implementation can be thought of as a couple of nested loops with lot of method calls from the same model.
Most of these methods take a complex hash created initially in the loop, modify it and pass it on to another method further in the loop which then processes it till we arrive at the final answer hash.
How should I go around unit testing my methods?
Best practice would suggest that you test the boundaries rather than the internal method calls.
Testing the inner workings of a class tend to lead to brittle tests that break even though the end result is what you want.
In this regard it would be best to test the input against the expected output and avoid testing how it got to the output.
There is an excellent talk by Sandi Metz on the subject here http://vimeo.com/48106365
It seems, that there are two totally different approaches to testing, and I would like to cite both of them.
The thing is, that those opinions were stated 5 years ago (2007), and I am interested, what has changed since then and which way should I go.
Brandon Keepers:
The theory is that tests are supposed to be agnostic of the
implementation. This leads to less brittle tests and actually tests
the outcome (or behavior).
With RSpec, I feel like the common approach of completely mocking your
models to test your controllers ends up forcing you to look too much
into the implementation of your controller.
This by itself is not too bad, but the problem is that it peers too
much into the controller to dictate how the model is used. Why does it
matter if my controller calls Thing.new? What if my controller decides
to take the Thing.create! and rescue route? What if my model has a
special initializer method, like Thing.build_with_foo? My spec for
behavior should not fail if I change the implementation.
This problem gets even worse when you have nested resources and are
creating multiple models per controller. Some of my setup methods end
up being 15 or more lines long and VERY fragile.
RSpec’s intention is to completely isolate your controller logic from
your models, which sounds good in theory, but almost runs against the
grain for an integrated stack like Rails. Especially if you practice
the skinny controller/fat model discipline, the amount of logic in the
controller becomes very small, and the setup becomes huge.
So what’s a BDD-wannabe to do? Taking a step back, the behavior that I
really want to test is not that my controller calls Thing.new, but
that given parameters X, it creates a new thing and redirects to it.
David Chelimsky:
It’s all about trade-offs.
The fact that AR chooses inheritance rather than delegation puts us in
a testing bind – we have to be coupled to the database OR we have to
be more intimate with the implementation. We accept this design choice
because we reap benefits in expressiveness and DRY-ness.
In grappling with the dilemma, I chose faster tests at the cost of
slightly more brittle. You’re choosing less brittle tests at the cost
of them running slightly slower. It’s a trade-off either way.
In practice, I run the tests hundreds, if not thousands, of times a
day (I use autotest and take very granular steps) and I change whether
I use “new” or “create” almost never. Also due to granular steps, new
models that appear are quite volatile at first. The valid_thing_attrs
approach minimizes the pain from this a bit, but it still means that
every new required field means that I have to change
valid_thing_attrs.
But if your approach is working for you in practice, then its good! In
fact, I’d strongly recommend that you publish a plugin with generators
that produce the examples the way you like them. I’m sure that a lot
of people would benefit from that.
Ryan Bates:
Out of curiosity, how often do you use mocks in your tests/specs?
Perhaps I'm doing something wrong, but I'm finding it severely
limiting. Since switching to rSpec over a month ago, I've been doing
what they recommend in the docs where the controller and view layers
do not hit the database at all and the models are completely mocked
out. This gives you a nice speed boost and makes some things easier,
but I'm finding the cons of doing this far outweigh the pros. Since
using mocks, my specs have turned into a maintenance nightmare. Specs
are meant to test the behavior, not the implementation. I don't care
if a method was called I just want to make sure the resulting output
is correct. Because mocking makes specs picky about the
implementation, it makes simple refactorings (that don't change the
behavior) impossible to do without having to constantly go back and
"fix" the specs. I'm very opinionated about what a spec/tests should
cover. A test should only break when the app breaks. This is one
reason why I hardly test the view layer because I find it too rigid.
It often leads to tests breaking without the app breaking when
changing little things in the view. I'm finding the same problem with
mocks. On top of all this, I just realized today that mocking/stubbing
a class method (sometimes) sticks around between specs. Specs should
be self contained and not influenced by other specs. This breaks that
rule and leads to tricky bugs. What have I learned from all this? Be
careful where you use mocking. Stubbing is not as bad, but still has
some of the same issues.
I took the past few hours and removed nearly all mocks from my specs.
I also merged the controller and view specs into one using
"integrate_views" in the controller spec. I am also loading all
fixtures for each controller spec so there's some test data to fill
the views. The end result? My specs are shorter, simpler, more
consistent, less rigid, and they test the entire stack together
(model, view, controller) so no bugs can slip through the cracks. I'm
not saying this is the "right" way for everyone. If your project
requires a very strict spec case then it may not be for you, but in my
case this is worlds better than what I had before using mocks. I still
think stubbing is a good solution in a few spots so I'm still doing
that.
I think all three opinions are still completely valid. Ryan and I were struggling with the maintainability of mocking, while David felt the maintenance tradeoff was worth it for the increase in speed.
But these tradeoffs are symptoms of a deeper problem, which David alluded to in 2007: ActiveRecord. The design of ActiveRecord encourages you to create god objects that do too much, know too much about the rest of the system, and have too much surface area. This leads to tests that have too much to test, know too much about the rest of the system, and are either too slow or brittle.
So what's the solution? Separate as much of your application from the framework as possible. Write lots of small classes that model your domain and don't inherit from anything. Each object should have limited surface area (no more than a few methods) and explicit dependencies passed in through the constructor.
With this approach, I've only been writing two types of tests: isolated unit tests, and full-stack system tests. In the isolation tests, I mock or stub everything that is not the object under test. These tests are insanely fast and often don't even require loading the whole Rails environment. The full stack tests exercise the whole system. They are painfully slow and give useless feedback when they fail. I write as few as necessary, but enough to give me confidence that all my well-tested objects integrate well.
Unfortunately, I can't point you to an example project that does this well (yet). I talk a little about it in my presentation on Why Our Code Smells, watch Corey Haines' presentation on Fast Rails Tests, and I highly recommend reading Growing Object Oriented Software Guided by Tests.
Thanks for compiling the quotes from 2007. It is fun to look back.
My current testing approach is covered in this RailsCasts episode which I have been quite happy with. In summary I have two levels of tests.
High level: I use request specs in RSpec, Capybara, and VCR. Tests can be flagged to execute JavaScript as necessary. Mocking is avoided here because the goal is to test the entire stack. Each controller action is tested at least once, maybe a few times.
Low level: This is where all complex logic is tested - primarily models and helpers. I avoid mocking here as well. The tests hit the database or surrounding objects when necessary.
Notice there are no controller or view specs. I feel these are adequately covered in request specs.
Since there is little mocking, how do I keep the tests fast? Here are some tips.
Avoid excessive branching logic in the high level tests. Any complex logic should be moved to the lower level.
When generating records (such as with Factory Girl), use build first and only switch to create when necessary.
Use Guard with Spork to skip the Rails startup time. The relevant tests are often done within a few seconds after saving the file. Use a :focus tag in RSpec to limit which tests run when working on a specific area. If it's a large test suite, set all_after_pass: false, all_on_start: false in the Guardfile to only run them all when needed.
I use multiple assertions per test. Executing the same setup code for each assertion will greatly increase the test time. RSpec will print out the line that failed so it is easy to locate it.
I find mocking adds brittleness to the tests which is why I avoid it. True, it can be great as an aid for OO design, but in the structure of a Rails app this doesn't feel as effective. Instead I rely heavily on refactoring and let the code itself tell me how the design should go.
This approach works best on small-medium size Rails applications without extensive, complex domain logic.
Great questions and great discussion. #ryanb and #bkeepers mention that they only write two types of tests. I take a similar approach, but have a third type of test:
Unit tests: isolated tests, typically, but not always, against plain ruby objects. My unit tests don't involve the DB, 3rd party API calls, or any other external stuff.
Integration tests: these are still focused on testing one class; the differences is that they integrate that class with the external stuff I avoid in my unit tests. My models will often have both unit tests and integration tests, where the unit tests focus in the pure logic that can be tested w/o involving the DB, and the integration tests will involve the DB. In addition, I tend to test 3rd party API wrappers with integration tests, using VCR to keep the tests fast and deterministic, but letting my CI builds make the HTTP requests for real (to catch any API changes).
Acceptance tests: end-to-end tests, for an entire feature. This isn't just about UI testing via capybara; I do the same in my gems, which may not have an HTML UI at all. In those cases, this exercises whatever the gem does end-to-end. I also tend to use VCR in these tests (if they make external HTTP requests), and like in my integration tests, my CI build is setup to make the HTTP requests for real.
As far as mocking goes, I don't have a "one size fits all" approach. I've definitely overmocked in the past, but I still find it to be a very useful technique, especially when using something like rspec-fire. In general, I mock collaborators playing roles freely (particularly if I own them, and they are service objects) and try to avoid it in most other cases.
Probably the biggest change to my testing over the last year or so has been inspired by DAS: whereas I used to have a spec_helper.rb that loads the entire environment, now I explicitly load just the class-under test (and any dependencies). Besides the improved test speed (which does make a huge difference!) it helps me identify when my class-under-test is pulling in too many dependencies.
I'm having a hard time learning how to implement appropriate testing with rspec and rails.
Speaking generally, how does one test the "hard cases" such as did a file get generated or was an image properly resized? Currently, to me it seems that unit testing is designed for testing the transformation of values rather than making sure data is processed and output appropriately.
TL;DR You should explore for different tools and don't shy away from the "hard cases" that may not seem like traditional "unit tests". The hard cases often are testable.
Testing is definitely a rabbit hole. From the surface, it seems so nice and clean, but as you get in to it, the rabbit hole goes quite far down, and this is one example: how do you test these things? You want to be confident that your code is doing the right thing, but you also don't want to create too complicated and unmanageable tests, and you don't want to test too fine-grained either.
However, to your specific questions, I do have some ideas you may wish to look in to.
For testing that a file got generated, you can check to see that initially the file did not exist (ruby has File.exists?) and then you can, after some method, check to see if it does exist. Of course you have questions like, "Does it have the right content?", "Did it finish to completion?", and you can test that stuff too by opening the file and checking it.
For the images, you probably can find facilities that allow you to check the properties of an image (perhaps Paperclip? Never used it but it's a well known gem). So you can do something like this (in sort-of psuedo code, because I don't know of a tool to do this):
it "resizes the image" do
img = Image.open_image("pic.png")
img[:size].should eq [100, 100]
img.close
resize_image
image = Image.open_image("pic.png")
imge[:size].should eq [25, 25]
img.close
end
Testing often relies on finding more and more helpful gems/tools to massage situations. "Unit" tests will, yes, only check the unit level code and they may be very simple, but not always. But then you start looking in to library specs, request specs, routing specs, acceptance tests, controller specs, etc. There are lot of tools out there and research is key.
But again, the examples you listed may not be unit tests in the way you think of. If your resizing or file generation is being done off of a Model, then yes it is a unit test, but you're no longer writing that simple code (like accessors and mutators). A lot of the time people new to thorough testing won't think that everything is testable, and it may not be, but if you play around and explore, you can often find a way to do so.
I understand that rspec is used to test with specific examples, but it seems to me that errors most times are of dynamic nature. Therefore, i'm having some doubts if unit testing is really useful for me ( i don't say that rspec is not useful of course).
I'm thinking that if i add a validation on a model, this enforces its behaviour. Since i already know that i will put it, what is the real point behind creating a test for it first ? After all, it will always pass if i don't change the validation (in which case i will notice of course). Provided that i'm the only developer, isn't that a little bit too much work for no real reason ?
Moreover, let's say that i have a test that specifies that user.name must be either 'Tom' or 'John'. My tests work great, because i specify user.name inside the test. However, in the real application, it may happen that name becomes 'Alex'. Rspec would not be able to enforce the behaviour, would it ?
And i would be left with a passing test, but an error.
What do you think about all that ? Are my concerns correct or i am not thinking it well ? I need to know whether i would get some strong benefits from messing with rspec, or it would mostly be a waste of time.
(Again i understand that rspec can be useful, but what about the matters that i specify here ?)
I'm thinking that if i add a validation on a model, this enforces its behaviour.
Adding validation to your model gives that model some behavior but does not enforce it. A behavior is only required when some other piece of code depends on it and will break if it changes. Until a behavior is used removing it would have no impact on your project and so nothing enforces that the behavior must be present.
Since i already know that i will put it, what is the real point behind creating a test for it first ? After all, it will always pass if i don't change the validation (in which case i will notice of course).
Writing tests, especially writing tests first, gives you an immediate use of your code. Something which requires a behavior to be present and which should fail quickly, reliably, and automatically if that behavior changes. Tests enforce the public interface to your code because otherwise you will change that interface and you will not notice.
Provided that i'm the only developer, isn't that a little bit too much work for no real reason ?
You may be the only person working on the project but you can't remember everything. Write tests so that next week you have something to make sure you don't violate the assumptions you made today.
Moreover, let's say that i have a test that specifies that user.name must be either 'Tom' or 'John'.
That is not specific enough to be a good test. You can test that "a user should be valid when user.name is 'Tom'" or "user.name must be included in ['Tom', 'John']" or even "a user should be invalid if user.name is 'Alex'". You cannot hope to write a test for all possible inputs to your application so you need to make intelligent choices about what to test. Test that valid inputs produce valid results. Test that invalid inputs fail in expected ways. Don't worry about testing all possible invalid inputs or invalid uses of your code.
If it is not valid for "user.name" to be "Alex" then perhaps you should test that the code calling your User object does not try to set its name to "Alex". If "Alex" is a valid name but your code failed anyway then you should write more robust code, better tests, and a test for the name "Alex" to make sure you fixed your User class to handle that name.
Perhaps most importantly, if you are writing tests first then they can actually drive you to design a better interface for your User class. One which more clearly expresses the behavior of the "name" attribute and discourages you from setting invalid names.
Tests are tests. They test things. They don't enforce things.
They are useful because you can see what is and isn't working in your application. When you override that name= setter to do something fancy and it breaks on a simple case that you had written a test for, that test just saved your ass. For simple cases like this, going without a test might be okay. It's really rare that you see 100% test coverage in non-open-source applications. Until you learn what you don't need to test, though, it's easier to just write tests for everything you can.
If you don't understand Test Driven Development or why you would test, I think you should Google around on the subject a bit and you can get a good taste of what there is out there and why you should use it (and you should).
Test cases, in my opinion, are sort of like documenting the requirements. We ensure that these requirements are met when we pass the tests. The first time it wont make sense, as we will be writing the code with requirements on mind. It is when we have to change code to incorporate something else also (or just refractor the code for performance), the tests really come into play. This time, we have to ensure that the previous requirements are also met while making the change i.e. the test cases do not fail. This way, by having tests, we are making a note of the requirements and making sure the requirements are met, when we are changing or refractor the code.
I've been writing tests for a while now and I'm starting to get the hang of things. But I've got some questions concerning how much test coverage is really necessary. The consensus seems pretty clear: more coverage is always better. But, from a beginner's perspective at least, I wonder if this is really true.
Take this totally vanilla controller action for example:
def create
#event = Event.new(params[:event])
if #event.save
flash[:notice] = "Event successfully created."
redirect_to events_path
else
render :action => 'new'
end
end
Just the generated scaffolding. We're not doing anything unusual here. Why is it important to write controller tests for this action? After all, we didn't even write the code - the generator did the work for us. Unless there's a bug in rails, this code should be fine. It seems like testing this action is not all too different from testing, say, collection_select - and we wouldn't do that. Furthermore, assuming we're using cucumber, we should already have the basics covered (e.g. where it redirects).
The same could even be said for simple model methods. For example:
def full_name
"#{first_name} #{last_name}"
end
Do we really need to write tests for such simple methods? If there's a syntax error, you'll catch it on page refresh. Likewise, cucumber would catch this so long as your features hit any page that called the full_name method. Obviously, we shouldn't be relying on cucumber for anything too complex. But does full_name really need a unit test?
You might say that because the code is simple the test will also be simple. So you might as well write a test since it's only going to take a minute. But it seems that writing essentially worthless tests can do more harm than good. For example, they clutter up your specs making it more difficult to focus on the complex tests that actually matter. Also, they take time to run (although probably not much).
But, like I said, I'm hardly an expert tester. I'm not necessarily advocating less test coverage. Rather, I'm looking for some expert advice. Is there actually a good reason to be writing such simple tests?
My experience in this is that you shouldn't waste your time writing tests for code that is trivial, unless you have a lot of complex stuff riding on the correctness of that triviality. I, for one, think that testing stuff like getters and setters is a total waste of time, but I'm sure that there'll be more than one coverage junkie out there who'll be willing to oppose me on this.
For me tests facilitate three things:
They garantuee unbroken old functionality If I can check that
nothing new that I put in has broken
my old things by running tests, it's
a good thing.
They make me feel secure when I rewrite old stuff The code I
refactor is very rarely the trivial
one. If, however, I want to refactor
untrivial code, having tests to
ensure that my refactorings have not
broken any behavior is a must.
They are the documentation of my work Untrivial code needs to be
documented. If, however, you agree
with me that comments in code is the
work of the devil, having clear and
concise unit tests that make you
understand what the correct behavior
of something is, is (again) a must.
Anything I'm sure I won't break, or that I feel is unnessecary to document, I simply don't waste time testing. Your generated controllers and model methods, then, I would say are all fine even without unit tests.
The only absolute rule is that testing should be cost-efficient.
Any set of practical guidelines to achieve that will be controversial, but here are some advices to avoid tests that will be generally wasteful, or do more harm than good.
Unit
Don't test private methods directly, only assess their effects indirectly through the public methods that call them.
Don't test internal states
Only test non-trivial methods, where different contexts may get different results (calculations, concatenation, regexes, branches...)
Don't assess things you don't care about, e.g. full copy on some message or useless parts of complex data structures returned by an API...
Stub all the things in unit tests, they're called unit tests because you're only testing one class, not its collaborators. With stubs/spies, you test the messages you send them without testing their internal logic.
Consider private nested classes as private methods
Integration
Don't try to test all the combinations in integration tests. That's what unit tests are for. Just test happy-paths or most common cases.
Don't use Cucumber unless you really BDD
Integration tests don't always need to run in the browser. To test more cases with less of a performance hit you can have some integration tests interact directly with model classes.
Don't test what you don't own. Integration tests should expect third-party dependencies to do their job, but not substitute to their own test suite.
Controller
In controller tests, only test controller logic: Redirections, authentication, permissions, HTTP status. Stub the business logic. Consider filters, etc. like private methods in unit tests, tested through public controller actions only.
Others
Don't write route tests, except if you're writing an API, for the endpoints not already covered by integration tests.
Don't write view tests. You should be able to change copy or HTML classes without breaking your tests. Just assess critical view elements as part of your in-browser integration tests.
Do test your client JS, especially if it holds some application logic. All those rules also apply to JS tests.
Ignore any of those rules for business-critical stuff, or when something actually breaks (no-one wants to explain their boss/users why the same bug happened twice, that's why you should probably write at least regression tests when fixing a bug).
See more details on that post.
More coverage is better for code quality- but it costs more. There's a sliding scale here, if you're coding an artificial heart, you need more tests. The less you pay upfront, the more likely it is you'll pay later, maybe painfully.
In the example, full_name, why have you placed a space between, and ordered by first_name then last_name- does that matter? If you are later asked to sort by last name, is it ok to swap the order and add a comma? What if the last name is two words- will that additional space affect things? Maybe you also have an xml feed someone else is parsing? If you're not sure what to test, for a simple undocumented function, maybe think about the functionality implied by the method name.
I would think your company's culture is important to consider too. If you're doing more than others, then you're really wasting time. Doesn't help to have a well tested footer, if the main content is buggy. Causing the main build or other developer's builds to break, would be worse though. Finding the balance is hard- unless one is the decider, spend some time reading the test code written by other team members.
Some people take the approach of testing the edge cases, and assume the main features will get worked out through usage. Considering getter/setters, I'd want a model class somewhere, that has a few tests on those methods, maybe test the database column type ranges. This at least tells me the network is ok, a database connection can be made, I have access to write to a table that exists, etc. Pages come and go, so don't consider a page load to be a substitute for an actual unit test. (A testing efficiency side note- if having automated testing based on the file update timestamp (autotest), that test wouldn't run, and you want to know asap)
I'd prefer to have better quality tests, rather than full coverage. But I'd also want an automated tool pointing out what isn't tested. If it's not tested, I assume it's broken. As you find failure, add tests, even if it's simple code.
If you are automating your testing, it doesn't matter how long it takes to run. You benefit every time that test code is run- at that point, you know a minimum of your code's functionality is working, and you get a sense of how reliable the tested functionality has been over time.
100% coverage shouldn't be your goal- good testing should be. It would be misleading to think a single test of a regular expression was accomplishing anything. I'd rather have no tests than one, because my automated coverage report reminds me the RE is unreliable.
The primary benefit you would get from writing a unit test or two for this method would be regression testing. If, sometime in the future, something was changed that impacted this method negatively, you would be able to catch it.
Whether or not that's worth the effort is ultimately up to you.
The secondary benefit I can see by looking at it would be testing edge cases, like, what it should do if last_name is "" or nil. That can reveal unexpected behavior.
(i.e. if last_name is nil, and first_name is "John", you get full_name => "John ")
Again, the cost-vs-benefit is ultimately up to you.
For generated code, no, there's no need to have test coverage there because, as you said, you didn't write it. If there's a problem, it's beyond the scope of the tests, which should be focused on your project. Likewise, you probably wouldn't need to explicitly test any libraries that you use.
For your particular method, it looks like that's the equivalent of a setter (it's been a bit since I've done Ruby on Rails) - testing that method would be testing the language features. If you were changing values or generating output, then you should have a test. But if you are just setting values or returning something with no computation or logic, I don't see the benefit to having tests cover those methods as if they are wrong, you should be able to detect the problem in a visual inspection or the problem is a language defect.
As far as the other methods, if you write them, you should probably have a test for them. In Test-Driven Development, this is essential as the tests for a particular method exist before the method does and you write methods to make the test pass. If you aren't writing your tests first, then you still get some benefit to have at least a simple test in place should this method ever change.