factory_girl_analyzer.rb

if ENV['FG_STATS']
  at_exit { require 'rubygems'; require 'pry'; binding.pry }
end

# Normal test helper code w/ Minitest

if ENV['FG_STATS']
  class TestInefficiencyAnalyzer
    def initialize(adapter)
      case adapter
      when :minitest
        @adapter = MinitestAdapter.new
      else
        raise 'Unrecognized adapter!'
      end
    end

    def start
      @adapter.start
    end

    def improvements
      @adapter.improvements
    end

    def report
      puts
      @adapter.improvements.each do |i|
        # TODO remove redundancy
        puts "In #{i[:test]}:"
        i[:improvements].each do |im|
          puts "\tAt #{im[:line]}: #{im[:from]} => #{im[:to]}"
        end
        puts
      end
      nil
    end

    class MinitestAdapter
      MinitestSpy = Module.new
      MinitestSpy.extend(Spy::API)

      attr_accessor :improvements

      def initialize
        @improvements = []
      end

      def start
        adapter = self
        MinitestSpy.on(Minitest, :run_one_method)
          .wrap do |r, test, method_name, *args, &block|
            improvement = ImprovementFinder.find_improvements(adapter, r.name, test, block)
            adapter.improvements << improvement if improvement
          end
      end

      # Returns boolean whether test passed
      def test_passes?(block)
        result = block.call
        result.passed?
      end
    end

    class ImprovementRun
      RunSpy = Module.new
      RunSpy.extend(Spy::API)

      attr_reader :inefficient, :efficient, :nth_call
      attr_accessor :in_call, :caller

      def initialize(adapter, test_block, inefficient, efficient, nth_call)
        @adapter = adapter
        @test_block = test_block
        @inefficient = inefficient
        @efficient = efficient
        @nth_call = nth_call
        @in_call = false
      end

      def run
        manage_call_recursion
        stub
        run_test
      ensure
        clean_up
      end

      private

      def manage_call_recursion
        run = self
        # Deal with #build calling create or #create calling build as well
        # as recursion. Only work with top-level calls
        [:create, :build].each do |sym|
          RunSpy.on(FactoryGirl, sym).wrap do |*args, &block|
            if run.in_call == false
              run.in_call = true
              block.call
              run.in_call = false
            end
          end
        end
      end

      def stub
        run = self
        call_count = 0
        FactoryGirl.define_singleton_method inefficient.name, -> (*args) {
          # recursionnnnn
          if run.in_call
            return inefficient.call(*args)
          end

          call_count += 1
          if call_count == run.nth_call
            # TODO: fix caller when recursive or composite call
            run.caller = caller[0]
            res = run.efficient.call(*args)
          else
            res = run.inefficient.call(*args)
          end
        }
      end

      def run_test
        if @adapter.test_passes?(@test_block)
          {
            line: self.caller[/\d+/],
            from: inefficient.name,
            to: efficient.name,
            #source: self.caller.sub(Rails.root.to_s, ''),
            #index: nth_call
          }
        end
      end

      def clean_up
        FactoryGirl.define_singleton_method inefficient.name, inefficient
        RunSpy.restore(:all)
      end
    end

    class ImprovementFinder
      FgSpy = Module.new
      FgSpy.extend(Spy::API)

      def self.find_improvements(adapter, test, method_name, block)
        new(adapter, test, method_name, block).find_improvements
      end

      # Find improvements in the given test, method, block
      def initialize(adapter, test, method_name, block)
        @adapter = adapter
        @test = test
        @method_name = method_name
        @block = block
        @improvements = []

        # Save original method bindings
        @fg_create = FactoryGirl.method(:create)
        @fg_build = FactoryGirl.method(:build)
        @fg_build_stubbed = FactoryGirl.method(:build_stubbed)
      end

      def find_improvements
        dry_run
        find_improvements_create
        find_improvements_build
        report
      end

      private

      # Perform a dry run of the test to figure out how many times
      # we call each inefficient method
      def dry_run
        in_spy = false # Don't count recursive/nested calls
        create_spy  = FgSpy.on(FactoryGirl, :create)
        build_spy   = FgSpy.on(FactoryGirl, :build)
        [create_spy, build_spy].each do |s|
          s.when    { !in_spy }
          s.before  { in_spy = true }
          s.after   { in_spy = false }
        end
        @block.call
        @dry_calls_create = create_spy.call_count
        @dry_calls_build  = build_spy.call_count
        FgSpy.restore(:all)
      end

      # Try substituting each call to the inefficient method with
      # the more efficient one. See if the tests still pass with
      # the substitution
      def find_improvements_create
        (1..@dry_calls_create).to_a.each do |idx|
          has_passed = try_create_to_build_stubbed(idx)
          # #build_stubbed is better than #build; use it if we can
          try_create_to_build(idx) if !has_passed
        end
      end

      def find_improvements_build
        (1..@dry_calls_build).to_a.each do |idx|
          try_build_to_build_stubbed(idx)
        end
      end

      def try_create_to_build(idx)
        find_improvement(@fg_create, @fg_build, idx)
      end

      def try_create_to_build_stubbed(idx)
        find_improvement(@fg_create, @fg_build_stubbed, idx)
      end

      def try_build_to_build_stubbed(idx)
        find_improvement(@fg_build, @fg_build_stubbed, idx)
      end

      def report
        if @improvements.any?
          {
            test: @test,
            method_name: @method_name,
            improvements: @improvements
          }
        end
      end

      # Stub out the nth call of the inefficient method with the
      # efficient one. See if the tests still pass
      def find_improvement(inefficient, efficient, nth_call)
        improvement = ImprovementRun.new(@adapter, @block, inefficient, efficient, nth_call).run
        @improvements << improvement if improvement
        !!improvement
      end
    end
  end

  analyzer = TestInefficiencyAnalyzer.new(:minitest)
  analyzer.start
end