dummy_rails_app

hash.rb

# lib/core_ext/hash.rb

class Hash
  # monkey-patch to temporarily
  # disabling the MyLib#print_config output
  def to_json
    ''
  end
end

my_lib.rb

# lib/my_lib.rb

class MyLib
  attr_accessor :config
  
  def initialize
    config = {}

    yield(config) if block_given?
  end
  
  def print_config
    "config: #{config.to_json}" # <= Monkey-patch applied here
  end
end

products_controller.rb

# app/controllers/products_controller.rb

class ProductsController < ApplicationController
  def index
    @products = {
      products: [
        # list of products
      ]
    }

    render json: @products # <= Side-effect of the monkey-patch
  end
end