Asserting on a JSON response in a Rails controller test with MiniTest

dummy_controller.rb

class DummyController < ApplicationController
  def do
    render json: { balance: 50 }
  end
end

dummy_controller_test.rb

require 'test_helper'

class DummyControllerTest < ActionController::TestCase
  test "should get do" do

    get :do

    json_response = JSON.parse(response.body)
    assert_equal 50, json_response["balance"]
  end
end