expect(response).to be_json_for Object

json_body_matcher.rb

module ContentTypeMatchers
  extend RSpec::Matchers::DSL

  matcher :be_content_type do |expected|
    match do |actual|
      expect(actual.content_type).to eq(expected)
    end

    failure_message_for_should do |actual|
      %Q(expected that response content type "#{actual.header['Content-Type']}" would be "#{expected}")
    end
    failure_message_for_should_not do |actual|
      %Q(expected that response content type "#{actual.header['Content-Type']}" would not be "#{expected}")
    end
  end
end

module JSONBodyMatchers
  extend RSpec::Matchers::DSL

  def differ
    @differ ||= if RSpec::Expectations.const_defined?(:DiffPresenter)
                  RSpec::Expectations::DiffPresenter
                else
                  RSpec::Expectations::Differ
                end
  end

  matcher :be_json_for do |expected|
    expected_json = expected.to_json
    expected      = JSON.parse(expected_json)

    match do |actual|
      expect(actual).to be_content_type 'application/json'
      result = JSON.parse(actual.body)
      expect(result).to eq(expected)
    end

    failure_message_for_should do |actual|
      message = %Q(expected that response body [#{actual.body}])
      message << %Q(\nwould be [#{expected_json}])
      message << "\nDiff:"
#     message << differ.new.diff_as_string(actual.body, expected_json)
      message << differ.new.diff_as_object(JSON.parse(actual.body), expected)
      message
    end

    failure_message_for_should_not do |actual|
      message = %Q(expected that response body [#{actual.body}])
      message << %Q(\nwould not be [#{expected_json}].)
    end
  end
end

RSpec.configure do |config|
  config.include ContentTypeMatchers
  config.include JSONBodyMatchers
end