Reproduction script for https://github.com/rspec/rspec-rails/issues/1668

rspec-rails-json-controller-params.rb

# Run this script with `ruby rspec-rails-json-controller-params.rb`
# It will spawn two processes: one using Minitest, one using RSpec.
if ARGV.empty?
  puts `ruby #{__FILE__} test`
  puts `ruby #{__FILE__} spec`
  exit
end

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  gem "rails", "5.0.0.1"
  gem "minitest", "~> 5.9.1"
  gem "rspec-rails", "~> 3.5"
end

require "action_controller/railtie"

class TestApp < Rails::Application
  config.root = File.dirname(__FILE__)
  config.session_store :cookie_store, key: "cookie_store_key"
  secrets.secret_token    = "secret_token"
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    post "/tests", to: "tests#create"
  end
end

class TestsController < ActionController::Base
  attr_accessor :boolean_attr

  def create
    self.boolean_attr = params.fetch(:boolean_attr)
    head :ok
  end
end

case ARGV.first
when "test"
  require "minitest/autorun"

  class BugTest < ActionDispatch::IntegrationTest
    def test_access_to_boolean_attributes_in_JSON_request
      post tests_path, params: { boolean_attr: true }, as: :json
      assert_same controller.boolean_attr, true
    end

    private

    def app
      Rails.application
    end
  end
when "spec"
  require "rspec/rails"
  require "rspec/autorun"

  RSpec.describe TestsController, type: :controller do
    it "has access to boolean attributes in JSON request" do
      post :create, params: { boolean_attr: true }, format: :json
      expect(controller.boolean_attr).to be(true)
    end

    it "works when patching `request` object" do
      request.content_type = 'application/json'
      post :create, params: { boolean_attr: true }, format: :json
      expect(controller.boolean_attr).to be(true)
    end
  end
end