Ruby o Rails Rspec - How to validate arguments when creating custom matchers - ruby-on-rails

Question

I would like to create a validation like the matcher have_http_status to the content_type.
I created the following matcher:
require 'rspec/expectations'
RSpec::Matchers.define :have_content_type do |expected|
match do |actual|
actual.content_type == expected
end
description do
"respond with content_type #{expected}"
end
end
However, I would like to check if the actual value is a response object. If not, I would like to give a message like the have_http_status, which would be:
Failure/Error: it { expect(legal_person).to have_http_status(200) }
expected a response object, but an instance of LegalPerson was received
# ./spec/controllers/legal_people_controller_spec.rb:105:in `block (5 levels) in <top (required)>'
So when I pass an object different from a request-response object, I would expect an error saying that a response object was expected.
It works without it but would be better if it shows an informative message saying what went wrong exactly.
Thanks in advance for the help.

Answer 1

You're trying to have 2 matchers under 1 name. I believe this is a bad practice, and there should be two matchers - one for content type, another one - for checking request/response type. So your tests should look like:
expect(response).to be_a(ActionDispatch::Response)
expect(response).to have_content_type('application/json')
Also, I don't see any problem of having just content type check. If the object passed does not have .content_type method, the matcher will throw corresponding error: Undefined method 'content_type' and you should be fine figuring out that you've passed wrong object.
But, if you are still sure you need to check two things in one matcher, check this:
RSpec::Matchers.define :have_content_type do |expected|
match do |actual|
request_or_response?(actual) && actual.content_type.to_s == expected
end
description do |actual|
if request_or_response?(actual)
"respond with content_type #{expected}"
else
"a response object, but an instance of #{actual.class} was received"
end
end
private
def request_or_response?(actual)
[Rack::Request, ActionDispatch::Response].any? do |klass|
actual.is_a?(klass)
end
end
end