How to mock properly an openssl object in rspec? - ruby

I have a method:
require 'openssl'
def extract_creds(data)
pfx = OpenSSL::PKCS12.new(data)
{ :certificate => pfx.certificate.to_pem, :key => pfx.key.to_pem }
rescue
# handle error
end
and i want to write a rspec example for it. How should i properly mock pfx object?

Why this may be the wrong question
You should generally use a mock when you want to:
Avoid testing system behavior outside the unit under test.
Avoid expensive operations, such inter-system tests.
Ensure that an object is called, but you don't care about the results.
In this case, it's not clear why you want to test this behavior, or what you expect the results to be, or why you think you might not get it. For the most part, testing a well-tested external library is not the right thing to do.
What I think the right question is
So, depending on what you really want to test, you may want to check:
Whether the method raises any exceptions.
Whether your method is actually called from some object that should call it.
In both cases, though, there seems to be no real benefit to mocking the library vs. including a real certificate as fixture data. Fixtures are better than mocks for actually exercising code.

Related

Rspec Double leaking to another example

I am testing a class that makes use of a client that makes external requests and I would like to mock this client, but verify that it gets called, however I am getting a double error.
My test looks like something like this:
describe '#execute' do
let(:attributes) { {foo: 'bar'} }
let(:client_double) { double('client', create: nil) }
let(:use_case) { described.class.new }
before do
allow(Client::Base).to receive(:new).and_return(client_double)
use_case.execute(attributes)
end
it 'creates something' do
expect(Something.find_by(foo: 'bar')).not_to be_nil
end
it 'calls client' do
expect(client).to have_received(:create).with('bar')
end
end
and the first example passes as expected, however rspec keeps breaking in the second example giving me this error:
#<Double "foo"> was originally created in one example but has leaked into another example and can no longer be used. rspec-mocks' doubles are designed to only last for one example, and you need to create a new one in each example you wish to use it for.
someone knows what I can do to fix it?
Reusing Fixtures with Let Methods
In this case, before is actually before(:each), which is reusing the client_double and attributes you defined with the #let helper method. The let commands make those variables functionally equivalent to instance variables within the scope of the described object, so you aren't really testing freshly-created objects in each example.
Some alternatives include:
Refactor to place all your setup into before(:each) without the let statements.
Make your tests DAMP by doing more setup within each example.
Set up new scope for a new #describe, so your test doubles/values aren't being reused.
Use your :before, :after, or :around blocks to reset state between tests, if needed.
Since you don't show the actual class or real code under test, it's hard to offer specific insights into the right way to test the object you're trying to test. It's not even clear why you feel you need to test the collaborator object within a unit test, so you might want to give some thought to that as well.
It turns out I was using a singleton as a client and haven't realized before, so it was trully class caching it through examples. To fix it all I did was mock the instantiate method instead of the new method and everything worked.
So in the end this worked:
allow(Client::Base).to receive(:instantiate).and_return(client_double)

How do I test a function's logic but ignore the method calls?

I'm writing a Rspec test for existing code that I've added some logic to that I want to ensure is working properly. I do not care about the returned values, just that the logic works on an object that I pass to it. For simplicity here is an example of very a basic function from within a class I have built:
def function_I_want_to_test(thing)
if thing > 0
function_a(thing)
else
function_b(thing)
end
end
function_a and function_b already have spec tests, so I don't really care what the return values are, but both function_a and function_b make API calls which I feel would make the rspec test a lot more complicated for testing only the logic contained within function_I_want_to_test.
I've gone through this page (https://blog.codeship.com/unit-testing-in-ruby/) reviewing the unit testing approach, and the explanations make sense, but when attempting to use allow and receive, it appears that the function is still wanting to be called so I'm assuming I'm not utilizing the functions correctly.
Essentially I want to treat my code as such, and have it return something arbitrary so it doesn't even call the function.
def function_I_want_to_test(thing)
if thing > 0
pp "a"
else
pp "b"
end
end
From my research, it appears the allow/expect is the way to go, but I'm assuming I'm not fully understanding the concept.
I guess the main question I have is, how does my rspec test know to "override" the functions (function_a and function_b) when testing function_I_want_to_test?
I know there are a few similar asked questions, but they didn't seem to answer how I was anticipating.

RSpec stubs apparently not cleaned up after test

I've been working to diagnose a test failure that only occurs on my master branch. Following is the relevant code, in simplified form.
There's a service:
class Service
attr_reader :traces
def initialize
#traces = []
end
def do_work
#traces << Thread.current.backtrace
# ... actual work ...
end
end
And a class that makes use of the service:
class Widget
def get_cached_service
puts("Getting a cached service!")
puts("Do I already have one? #{!!#service}")
#service ||= make_service
end
def make_service
puts("Making a service!")
Service.new
end
end
I have a test (that lives in a file widget_spec.rb) that fails intermittently. This test creates an instance of Widget and calls get_cached_service. I see the Getting a cached service! message on the console, followed by Do I already have one? false, but I don't see the Making a service! message.
Furthermore, when I examine the traces attribute of the returned Service object, I find stack traces originating from other tests in my project (eg. foo_spec.rb, bar_spec.rb, etc).
In a few different places I find code like:
allow_any_instance_of(Widget)
.to receive(:make_service).and_return(whatever)
The other tests whose stack traces I find are likely stubbing make_service like this. But it appears that the stubbing is not being undone after those tests, as should always happen according to my understanding.
Is there any reason, other than a bug in rspec, that could cause a stub not to be reset at the end of a test?
The stub is almost certainly being cleared, but you’ve cached the fake instance in get_cached_service. Nothing clears the cached value in #service, and RSpec (rightfully) doesn’t know about it. As such, stubbing make_service is not enough if tests call get_cached_service. You have a few options:
Always stub get_cached_service instead of, or in addition to, make_service
Provide a way to clear the cached value which is called after each test.
Make the caching configurable in some way, or a wrapper around the actual implementation, such that the caching does not occur in test code.
I realise this is quite late to answer, but for posterity for anyone who reads this:
Use rspec bisect to figure out if there is a consistent test ordering that causes failure, then start ripping code out until you're left with only the bit that breaks.
I can't remember a case where RSpec is at fault - almost invariably, somewhere there is a class variable that isn't getting cleared, or someone is manually playing with a class with something like define_method. Occasionally it might be happening in a gem.
Make sure everything is cleared after every test in your spec_helper - clear the Rails cache, clear ActionMailer deliveries, return from Timecop freezes, etc.
Anything directly RSpec-related should clear itself in theory, because it's designed to integrate into RSpec, and is probably the least likely explanation in general.

RSpec: testing AR finders without hitting the database

How would I test the following finder with RSpec?
def self.find_by_mbid(mbid)
super(mbid.downcase())
end
The only way I see that is possible would be storing it in the database beforehand, which I'd like to avoid, as this is a unit test. I don't see how to return a mock here, since super is pretty much inaccessible to RSpec.
Is there a better way of doing this? Or are unit tests too low-level for this sort of thing?
You could mock this if you're willing to change the implementation, but I recommend spec'ing finders with the database.

Should I open up a class's instance variables just for test validation?

I'm new to BDD, and I'm finding alot of instances where I'm adding instance variables to attr_accessor only so that my tests have an easy way to validate whether they are in the state that they should be in. But this feels a little dirty because no other class needs this information, and so I'm only making it public for the tests. Is this standard or a sign of bad design?
For example I have a collection class which stores an object, and then commits it to a batch array. At the end of the import, the batch array is used to make a batch insert into the database. But there is no need to check on the state of the batch at any point. But in testing I'm wanting to make sure that the batch is in the state that I think it is, and so am opening up that variable for inspection. Is the fact that it's not being checked within the code the real problem?
Is using instance_variable_get an option for you?
>> class Foo
.. def initialize
.. #foo = 'bar'
.. end
.. end #=> nil
>> Foo.new.instance_variable_get(:#foo) #=> "bar"
DON'T Do That!
This is going too deep. See the comments from #Andy and #Michael in the thread on the other 'accepted' answer
Don't write unit tests that look inside the code unit. If it's not something you can see from the external interfaces to the object then it doesn't need to be unit tested. You are going past how the code behaves into how it implements that behavior, and you don't want tests that go down to that level as they don't provide any real value in terms of proving that the code does what it should.
Just consider how many tests you might have to update if someone re-factors that code and in order to make it more readable changes the internal names of things.. or maybe finds a better way of doing whatever and all the instance variables get altered.. The code unit could still be working perfectly fine, but the unit tests would fail..
Alternatively if a change was made that adjusts how the internal variables report out to the interface, the code could effectively be broken, but the tests that are looking at the internal values of the instance variables would not report any failure.

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