What should I test/specify?

Ok, so here’s the scenario. I have a top-level module, with a method
called
load_file. It should take a file name, get the YAML module (Syck) to
parse
it, and then send the result to a class, which should convert that
result
into a series of objects.

I’m not sure what specs, if any, I should write for load_file. I can get
into the nitty gritty details of exactly what methods it should be
calling,
but that seems brittle. I can skip all that and just make assertions
about
the final series of objects, but I’d rather put those specs on the class
that’s actually doing the conversion.

Suggestions? Here’s the code that I (think I) want to drive out:

module BTree
def self.load_file file_name
raw = YAML::load_file file_name
tree = BehaviorTreeCreator.new(raw).create
end
end

If you’re writing a unit test for a method, the general rule of thumb
is to test what the method itself does. That sounds tautological, but
it’s meant to define the boundary of what you should and shouldn’t
care about.

In this case, you only care about the fact that YAML::load_file is
called, and that BehaviorTreeCreator.new is then called with the
result of that, and that that result has create invoked on it.
That’s it: if those three things happen, then this method is working
as you expect.

Your unit tests for BehaviorTreeCreator.new and .create will probably be
richer.

~ jf

John F.
Principal Consultant, BitsBuilder
LI: http://www.linkedin.com/in/fjsquared
SO: http://stackoverflow.com/users/75170/

On Oct 30, 2010, at 11:40 AM, Andrew W. wrote:

end
end

One approach would be:

describe BTree do
describe “::load_file” do
let(:filename) { ‘/tmp/btree_example.yml’ }
let(:content) { “—\na: 1\n” }
before { File.open(filename,‘w’) {|f| f.write content } }
after { File.delete filename }

it "reads and parses the content of the file" do
  BTree.load_file(filename).should 

eq(BehaviorTreeCreator.new(content).create
end
end
end

Assuming there are specs for BehaviorTreeCreator.new(content).create,
then this tells the story pretty well without being terribly invasive.

WDYT?

David

On Sat, Oct 30, 2010 at 12:46 PM, David C.
[email protected]wrote:

the final series of objects, but I’d rather put those specs on the class

 BTree.load_file(filename).should

David


rspec-users mailing list
[email protected]
http://rubyforge.org/mailman/listinfo/rspec-users

I like this, though it’s missing a YAML::load(content). I.e.,

BTree.load_file(filename).should
eq(BehaviorTreeCreator.new(YAML::load content).create

On 30 October 2010 14:40, Andrew W. [email protected] wrote:

Suggestions? Here’s the code that I (think I) want to drive out:

module BTree
def self.load_file file_name
raw = YAML::load_file file_name
tree = BehaviorTreeCreator.new(raw).create
end
end

Its not obvious what specs to write for load_file because load_file is
poorly named. It does far more than load a file. If you write your
specs
for load file and read them, they won’t make sense e.g.

load_file should use YAML (why should it use YAML, and what happens if
the
file isn’t YAML
load_file should create a behaviour tree (why should it create a TREE)

Perhaps BTree only needs a yaml_to_tree, and you can pass the yaml into
the
method. If this was the case you might spec the following:
what happens if you pass invalid YAML
what happens if you pass valid YAML
what happens if you pass nothing

Generally if a method is hard to spec, then its smelly, there is
something
wrong with it, it needs work

HTH

Andrew

Yeah, that’s about what I figured, thanks. This is what I came up with:

require ‘spec_helper.rb’
require ‘yaml’

describe “BTree” do
describe “.load_file” do
context “when the file exists” do
before(:all) { File.open(“test_file.yaml”, ‘w’) {|f| } }
after(:all) { File.delete “test_file.yaml”}

  after(:each) { BTree.load_file "test_file.yaml" }
  it "parses the yaml in the file" do
    YAML.stub!(:load_file).and_return(:foo)

YAML.should_receive(:load_file).with(“test_file.yaml”).and_return(:foo)
end

  it "converts the raw data into a tree" do
    fake_creator = Object.new

    fake_creator.stub! :create
    YAML.stub!(:load_file).and_return(:data)
    BehaviorCreator.stub!(:new).and_return :tree

    BehaviorCreator.should_receive(:new).with(:data).and_return

fake_creator
fake_creator.should_receive :create
end
end

context "when the file doesn't exist" do
  it "raises an error" do
    lambda { BTree.load_file "non_existent.yaml" }.should 

raise_error
end
end
end
end

On Sat, Oct 30, 2010 at 9:54 PM, Andrew P. remove[email protected]
wrote:

the final series of objects, but I’d rather put those specs on the class

method. If this was the case you might spec the following:

[email protected]
http://rubyforge.org/mailman/listinfo/rspec-users

An interesting perspective. The purpose of the behavior tree module is
to
provide a simple, standard way to represent behaviors in a plain-text
format. I’m borrowing YAML because it seems like a good, lightweight
approach. I’m using load_file (and load) to mirror YAML::load_file (and
YAML::load). I’ll definitely take some of your ideas into consideration,
thanks.

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