To expand further.
If I'd continued using position arguments and changed from:
def parse(body)
to
def parse(body, headers)
the instance double could calls to this were using the correct number of
arguments.
Alternatively if I was already using keyword arguments and added another
one:
def parse(body:)
to
def parse(body:, headers: {})
it would also get picked up.
It's only because passing keywords arguments to a method can be interpreted
as either a single hash or multiple arguments that this isn't picked up.
Steve.
On Tuesday, 19 September 2017 14:33:22 UTC+8, Steven Webb wrote:
>
> Thank you.
>
> I guess I was hoping that when the instance double verified that the
> message matches the method signature it would determine that I was trying
> to use keyword arguments instead of a hash.
>
> Steve.
>
> On Tuesday, 19 September 2017 14:20:10 UTC+8, Myron Marston wrote:
>>
>> What goal do you have in mind for this test? From the examples you gave,
>> it looks like you are only testing how RSpec’s verifying doubles work. For
>> example, this expectation:
>>
>> expect(html).to respond_to(:parse).with_keywords(:body, :headers)
>>
>> …isn’t exercising your code at all, because you’ve declared html as a
>> test double, so it’s just testing how doubles work. If you’re trying to
>> test the HTML class, you should not use a double in its place. Test doubles
>> are intended for when you want to control the environment in which you test
>> something, by replacing some collaborators with fake versions. They’re not
>> intended to ever replace the thing you are testing—once you do that, you’re
>> no longer testing the thing.
>>
>> Myron
>>
>>
>> On Mon, Sep 18, 2017 at 11:03 PM, Steven Webb <[email protected]>
>> wrote:
>>
>>> I'm having trouble testing a method signature change from taking a
>>> single argument (a hash) to using keyword arguments. I've created a
>>> contrived example of HTML parsing to simplify things (I'm not actually
>>> writing a html parser):
>>>
>>> class HTML
>>> def parse(body) # body is a hash
>>> ...
>>> end
>>> end
>>>
>>> I want to update it so that it can take an optional headers argument. It
>>> becomes:
>>>
>>> class HTML
>>> def parse(body: , headers: {}) # body and headers are both hashes
>>> end
>>> end
>>>
>>> In a related unit test of a different class I'm using something like
>>> this:
>>>
>>> RSpec.describe "calling the parser" do
>>> let(:html) { instance_double("HTML", parse: nil) }
>>> let(:body) { double("body") }
>>> let(:headers) { double("headers") }
>>>
>>> before { html.parse(body: body, headers: headers) }
>>>
>>> it "allows passing optional headers" do
>>> expect(html).to have_received(:parse).with(body: body, headers:
>>> headers)
>>> end
>>> end
>>>
>>> The problem I've got is that this test passes before updating the HTML
>>> class. After updating the HTML class it correctly detects the keywords as
>>> arguments and passes. Before it incorrectly determines the keywords are the
>>> "body" hash and passes. Both are valid ruby, but the method signature has
>>> changed (at least to me, possibly not to the VM). I tried:
>>>
>>> it "allows an optional headers argument" do
>>> expect(html).to respond_to(:parse).with_keywords(:body, :headers)
>>> end
>>>
>>> but that fails (presumably the instance double is using method_missing).
>>>
>>> 1) calling the parser allows an optional headers argument
>>> Failure/Error: expect(html).to
>>> respond_to(:parse).with_keywords(:body, :headers)
>>> expected #<InstanceDouble(HTML) (anonymous)> to respond to :parse
>>> with keywords :body and :headers
>>> # ./spec/keyword_args_spec.rb:40:in `block (2 levels) in <top
>>> (required)>'
>>>
>>> Can anyone explain how I should be testing this correctly?
>>>
>>> Thanks
>>>
>>> Steve.
>>>
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>>
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