This will extract any test failures into a separate log file for rspec. Useful for trying to get debug info on large test runs or flakey specs on CI

latest_test_failure.rb

module LatestTestFailure
  class << self
    def around(example)
      Rails.logger.info start_log(example.location)
      example.run
      Rails.logger.info end_log(
        example.location,
        example.exception ? "FAILED" : "PASSED"
      )
    end

    def after_suite
      File.write("log/latest_test_failures.log", "")
      failed_specs = grep_test_log(end_log(".*", "FAILED"))
      failed_specs.each_line do |line|
        end_log_line = capture_grep_end_line(line)
        start_log_line_number =
          grep_test_log(start_log(end_log_line[:spec_location]))
            .split(":")
            .first

        system(
          "sed -n " \
          "'#{start_log_line_number},#{end_log_line[:number]}p;$a\\\\' " \
          "log/test.log " \
          ">> " \
          "log/latest_test_failures.log"
        )
      end
    end

    def start_log(location)
      "RUN #{run_key} START TEST: #{location}"
    end

    def end_log(location, pass_fail = nil)
      "RUN #{run_key} END TEST: #{location} #{pass_fail}"
    end

    def capture_grep_end_line(line)
      line.match(%r{
        (?<number>\d+):
        RUN\s(?<run_key>.*)\sEND\sTEST:
        \s
        (?<spec_location>.*)
        \s
        (?<pass_fail>PASSED|FAILED)
      }x)
    end

    def grep_test_log(pattern)
      `grep -n "#{pattern}" log/test.log`
    end

    def run_key
      @run_key ||= SecureRandom.alphanumeric(5)
    end
  end
end

RSpec.configure do |config|
  config.around do |example|
    LatestTestFailure.around(example)
  end

  config.after(:suite) do
    if ENV["CI"] != "0" && ENV["LOG_LATEST_TEST_FAILURE"] != "0"
      LatestTestFailure.after_suite
    end
  end
end