RSpec test to ensure that the Oj gem is working in a Rails application

oj_spec.rb

# frozen_string_literal: true

require 'rails_helper'

# This test makes sure that Oj is used to parse and generate all JSON.
# Your application needs to call: Oj.optimize_rails
# See: https://github.com/ohler55/oj/blob/develop/pages/Rails.md#notes

RSpec.describe 'Oj gem' do
  it 'uses OJ to parse and generate JSON' do
    traced_calls = []
    tracer = TracePoint.new(:c_call) do |tp|
      traced_calls << [tp.defined_class, tp.method_id]
    end
    tracer.enable { 123.to_json }
    expect(traced_calls).to include [Oj::Rails::Encoder, :encode]

    traced_calls = []
    serializer = YourSerializerClass.new(build(:your_factory))
    tracer.enable { serializer.to_json }
    expect(traced_calls).to include [Oj::Rails::Encoder, :encode]

    traced_calls = []
    tracer.enable { JSON.parse('{"foo": 123}') }
    # If Oj is not loaded, this will be: "[[Class, :new], [JSON::Ext::Parser, :initialize], ...
    expect(traced_calls.to_s).to eq '[[#<Class:JSON>, :parse]]'

    expect do
      JSON.parse('{"a":x123}')
    end.to raise_error(
      JSON::ParserError,
      "unexpected character (a) at line 1, column 6 [parse.c:705] in '{\"a\":x123}"
    )
  end
end