Help with Writing Meaningful Specs

Testing RSpec
1

Hello all,

In yet another attempt to learn Ruby on Rails and Rspec I have started
writing a simple life streaming app with will aggregate feeds from
several
places and save them in a database for later use.

An internet search eventually led me to the following method for looping
through the feeds in the database, getting the contents of the URL and
then
passing this into another model to prepare and save it.

def self.cache_all
feeds = self.find(:all)

for feed in feeds
xml = REXML::Document.new Net::HTTP.get(URI.parse(feed.url))
xml.elements.each ‘//item’ do |item|
Item.prepare_and_save(feed, item)
end
end
end

Problems are now beginning to arise when trying to write the specs for
this
method. I started from scratch slowly building up the specs but it has
led
to an awful amount of mocks and stubs, and I am not even sure whether
they
are asking the correct things of the method.

Can anyone give me some pointers on how to write useful, meaningful
specs
for this method?

The other thing I have found is that I seem to have incorrectly stubbed
xml.elements.each meaning that the contents of the block are never
called,
how should I be specifying this behavior?

I have pastied the complete code for the Feed model, the spec and a
little
helper at: Parked at Loopia

Thanks in advance,

Andy

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2

On 27 May 2008, at 12:44, andypearson wrote:

xml = REXML::Document.new Net::HTTP.get(URI.parse(feed.url))

It won’t make the problem go away, but you can certainly reduce the
blizzard of intermediate stubs by pulling this chain out into its own
method (e.g. fetch_xml_from_url) and stubbing that method once in your
cache_all spec.

it has led to an awful amount of mocks and stubs, and I am not even
sure whether they
are asking the correct things of the method.
Can anyone give me some pointers on how to write useful, meaningful
specs
for this method?

What part of its behaviour do you care about? (Refactoring into more
fine-grained methods might help again here.) It seems as though all
you’re interested in is that 1. the feed URLs get fetched from the
database, 2. the feed contents get fetched from the URLs, and 3.
Item.prepare_and_save gets called for each item in each feed. So,
ideally, that’s what your specs for this method should be saying.

The other thing I have found is that I seem to have incorrectly
stubbed
xml.elements.each meaning that the contents of the block are never
called,
how should I be specifying this behavior?

Use #and_yield, not #and_return. (And you might as well use an actual
mock, rather than [@element], since you’re stubbing the only method
you plan to call on it.)

Cheers,
-Tom

3

On 27 May 2008, at 12:44, andypearson wrote:

for this method?
Hi Andy

I think the problem comes from two things - trying to specify the
details of an algorithm instead of checking it transforms the data
correctly, and having too much logic in a class method.

To take some Feed-specific logic out, try making an accessor method,
such as Feed#uri (I can’t think of a good name for it), then you could
replace one line with this:

xml = REXML::Document.new = Net::HTTP.get(feed.uri)

Alternatively, go one step further and have a method in Feed that does
the Net::HTTP.get, so you could write this:

xml = feed.xml_source

Obviously you will still need the corresponding specs in the Feed
instance methods, but at least you’ve encapsulated the logic related
to fetching the URI/XML.

The other thing is the “item” elements. I don’t know what
xml.elements.each yields, but I’m guessing it’s either plain text
(XML) or some REXML object. If it’s plain XML fine, but if it’s an
REXML object, you don’t want your code depending on that (you’re tying
yourself down to a specific library). Instead, consider parsing the
XML in Feed.cache_all. I’m imagining something like this:

feed.prepare_and_save_item(:item_attr_1 => “foo”,
:item_attr_2 => “bar”,
…)

The other thing I have found is that I seem to have incorrectly
stubbed
xml.elements.each meaning that the contents of the block are never
called,
how should I be specifying this behavior?

Just noticed that Tom replied and pointed out the issue. But if you
refactor the code like I describe above, you can avoid the issue.
Just stub feed.xml_source (or whatever) to return some sample valid
feed XML, and check that Feed.cache_all correctly extracts the item
data.

I can’t say that my way is better or worse than the way you are going
about it. But I (where possible) I always test the output of third-
party libraries rather than my use of them. It avoids loads of stubs
that don’t, in any case, prove you’re using the library correctly so
you can see immediately if your code is likely to work in the wild.

Hope this helps

Ashley

–
http://www.patchspace.co.uk/