Minitest helper to compare code with benchmark-ips

performance_helpers.rb

require 'benchmark/ips'

module PerformanceHelpers
  BENCHMARK_DURATION = 1
  BENCHMARK_WARMUP = 1
  BASELINE_LABEL = "Baseline"
  CODE_TO_TEST_LABEL = "Code"


  # Usage:
  #
  #     baseline = -> { <some baseline code> }
  #
  #     assert_slower_by_at_most 2, baseline: baseline do
  #       <the code you want to compare against the baseline>
  #     end
  def assert_slower_by_at_most(threshold_factor, baseline:, baseline_label: BASELINE_LABEL, code_to_test_label: CODE_TO_TEST_LABEL, &block_to_test)
    result = Benchmark.ips do |x|
      x.config(time: BENCHMARK_DURATION, warmup: BENCHMARK_WARMUP)
      x.report(code_to_test_label, &block_to_test)
      x.report(baseline_label, &baseline)
      x.compare!
    end

    baseline_result = result.entries.find { |entry| entry.label == baseline_label }
    code_to_test_result = result.entries.find { |entry| entry.label == code_to_test_label }

    times_slower = baseline_result.ips / code_to_test_result.ips
    assert times_slower >= 1, "Actually, '#{code_to_test_label}' was faster by a factor of #{1 / times_slower}"
    assert times_slower < threshold_factor, "Expecting #{threshold_factor} times slower at most, but got #{times_slower} times slower"
  end
end