Failing RSpec test with strong parameters - ruby-on-rails-5

Question

I am migrating my Rails 4 app (still using protected attributes gem) to Rails 5.1.4. In the course of this action, I need to rewrite a lot of code to replace protected attributes with strong parameters.
I am currently stuck on one specific controller where my RSpec tests fail, and I don't know how to implement the controller and test logic such that things are correct and tests pass.
The app has an admin backend where users can add (and thus upload) photos to an album. The respective Admin::PhotosController handles the photos of an album.
Here's the relevant exerpt from my app:
def create
# #organizer_account is set by an before_filter
#album = #organizer_account.albums.find_by_id(params[:album_id])
#photo = #album.photos.new(photo_params)
#photo.organizer_account_id = #organizer_account.id
authorize! :create, #photo
respond_to do |format|
if #photo.save
format.html {
render :json => [#photo.to_jq_file].to_json, :content_type => 'text/html', :layout => false
}
format.json {
files = [ #photo.to_jq_file ]
render :json => {:files => [#photo.to_jq_file] }, :status => :created, :location => admin_album_photo_path(#album, #photo)
}
else
format.html {
render action: "new"
}
format.json {
render json: #photo.errors, status: :unprocessable_entity
}
end
end
end
I have defined the following strong parameters:
private
def photo_params
params.require(:photo).permit(:id, :album_id, :organizer_account_id, :file)
end
The failing RSpec test is as follows:
require 'spec_helper'
describe Admin::PhotosController, :type => :controller do
render_views
describe "post 'create'" do
describe "with valid parameters" do
before(:each) do
#organizer_account = FactoryBot.create(:organizer_account)
#user = FactoryBot.create(:user)
#user.organizer_account_id = #organizer_account.id
#user.add_role :admin, #organizer_account
#user.save
sign_in #user
#album = #organizer_account.albums.create(:title => "Album 1")
#photo_attrs = FactoryBot.attributes_for(:photo)
request.env["HTTP_REFERER"] = new_admin_album_path
controller.request.host = #organizer_account.subdomain + ".lvh.me"
end
it "should create a new photo record", :focus => true do
lambda {
post :create, params: {:photo => #photo_attrs, :album_id => #album.id }
}.should change(#organizer_account.albums.find_by_id(#album.id).photos, :count).by(1)
end
end
end
end
I strongly assume that the issue is in parameters are a) passed
post :create, params: {:photo => #photo_attrs, :album_id => #album.id }
and then processed
#photo = #album.photos.new(photo_params)
While the params hash passed by the test has all the required entries
params: {"photo"=><ActionController::Parameters {"file"=>[#<ActionDispatch::Http::UploadedFile:0x00000010dd7560 #tempfile=#<Tempfile:C:/Users/PATRIC~1/AppData/Local/Temp/RackMultipart20180520-11424-avge07.gif>, #original_filename="image6.gif", #content_type="image/gif", #headers="Content-Disposition: form-data; name=\"photo[file][]\"; filename=\"image6.gif\"\r\nContent-Type: image/gif\r\nContent-Length: 46844\r\n">]} permitted: false>, "album_id"=>"1561", "controller"=>"admin/photos", "action"=>"create"}
the photo_params is empty:
photo_params: {}
Update #1: Definition of factory for photo
FactoryBot.define do
factory :photo, :class => Photo do
file Rack::Test::UploadedFile.new(Rails.root + 'spec/fixtures/photos/apfelkuchen.jpg', "image/jpg")
end
end
Update #2: Photo model with file attachment and image processing config
class Photo < ActiveRecord::Base
require 'rmagick'
include Magick
belongs_to :album
belongs_to :organizer_account
before_destroy { |photo| photo.file.destroy }
validates :album_id, :presence => true
validates :organizer_account_id, :presence => true
has_attached_file :file,
# The following tyles and convert options lead to breaking RSpec tests. If commented, RSpec tests pass.
:styles => {
:mini => "50x50#",
:thumb => "160x160#",
:large => "1200x1200>"
},
:convert_options => {
:mini => "-quality 75 -strip",
:thumb => "-quality 75 -strip"
}
validates :file, :presence => true
end