Why rack/test is combining hashes into one when performing POST or PUT operations - ruby-on-rails-3

Question

In my rspec test, I defined the following array of hashes and performed a POST:
body = {:event => { :invitations_attributes =>
[ {:recipient_id => 40}, {:email => 'a#a.com'}, {:facebook_id => 123456789} ] } }
post "#{#url}.json", body.reverse_merge(:auth_token => #token)
Based on the above, I expected the Rails server to receive "invitations_attributes" as an array of hashes. However, the developer.log file has the following:
Parameters: {"auth_token"=>"RSySKfN2L8b5QPqnfGf7", "event"=>{"invitations_attributes"=>
[{"recipient_id"=>"40", "email"=>"a#a.com", "facebook_id"=>"123456789"}]}}
(In the parameters above, "invitation_attributes" array contains only 1 hash.)
The following curl statement:
curl -X POST -H "Content-type: application/json" http://localhost:3000/api/v1/events.json -d '{"auth_token":"RSySKfN2L8b5QPqnfGf7","event":{"invitation_attributes":[{"recipient_id":40},{"email":"a#a.com"},{"facebook_id":123456789}]}}'
results in Rails' receiving the array of hashes intact, as evidenced by the log file entry below.
Parameters: {"auth_token"=>"RSySKfN2L8b5QPqnfGf7", "event"=>{"invitation_attributes"=>
[{"recipient_id"=>40}, {"email"=>"a#a.com"}, {"facebook_id"=>123456789}]}}
Rack/test is exhibiting this behavior for PUT operations as well as POST.
Why is rack/test combining the 3 hashes into 1 rather than sending the array exactly as it is defined? Is there a setting which will cause rack to exhibit the behavior I expected?

Answer 1

One workaround is to ensure that each hash contains each key by inserting nil value placeholder keys as follows:
body = {:event => { :invitations_attributes => [
{:recipient_id => 40, :recipient_email => nil, :recipient_facebook_id => nil},
{:recipient_email => user.email, :recipient_id => nil, :recipient_facebook_id => nil},
{:recipient_facebook_id => new_unused_facebook_id, :recipient_email => nil, :recipient_id => nil} ] } }
The hash above does cause the server to receive 3 separate hashes within the array. However, inserting placeholder keys is inconvenient and should not be required. Furthermore, scenarios where a controller acts differently based on the presence of a such a key (albeit uncommon), cannot be tested.