brew/Library/Homebrew/dev-cmd/update-test.rb

#:  * `update-test` [`--commit=<commit>`] [`--before=<date>`] [`--keep-tmp`]:
#:    Runs a test of `brew update` with a new repository clone.
#:
#:    If no arguments are passed, use `origin/master` as the start commit.
#:
#:    If `--commit=<commit>` is passed, use `<commit>` as the start commit.
#:
#:    If `--before=<date>` is passed, use the commit at `<date>` as the
#:    start commit.
#:
#:    If `--to-tag` is passed, set HOMEBREW_UPDATE_TO_TAG to test updating
#:    between tags.
#:
#:    If `--keep-tmp` is passed, retain the temporary directory containing
#:    the new repository clone.

module Homebrew
  module_function

  def update_test
    ENV["HOMEBREW_UPDATE_TO_TAG"] = "1" if ARGV.include?("--to-tag")

    cd HOMEBREW_REPOSITORY
    start_commit = if commit = ARGV.value("commit")
      commit
    elsif date = ARGV.value("before")
      Utils.popen_read("git", "rev-list", "-n1", "--before=#{date}", "origin/master").chomp
    else
      Utils.popen_read("git", "rev-parse", "origin/master").chomp
    end
    start_commit = Utils.popen_read("git", "rev-parse", start_commit).chomp
    end_commit = Utils.popen_read("git", "rev-parse", "HEAD").chomp

    puts "Start commit: #{start_commit}"
    puts "End   commit: #{end_commit}"

    mktemp("update-test") do |staging|
      staging.retain! if ARGV.keep_tmp?
      curdir = Pathname.new(Dir.pwd)

      oh1 "Setup test environment..."
      # copy Homebrew installation
      safe_system "git", "clone", "--local", "#{HOMEBREW_REPOSITORY}/.git", "."

      # set git origin to another copy
      safe_system "git", "clone", "--local", "--bare", "#{HOMEBREW_REPOSITORY}/.git", "remote.git"
      safe_system "git", "config", "remote.origin.url", "#{curdir}/remote.git"

      # force push origin to end_commit
      safe_system "git", "checkout", "-B", "master", end_commit
      safe_system "git", "push", "--force", "origin", "master"

      # set test copy to start_commit
      safe_system "git", "reset", "--hard", start_commit

      # update ENV["PATH"]
      ENV["PATH"] = "#{curdir}/bin:/usr/local/bin:/usr/bin:/bin"

      # run brew update
      oh1 "Running brew update..."
      safe_system "brew", "update", "--verbose"
      actual_end_commit = Utils.popen_read("git", "rev-parse", "master").chomp
      if start_commit != end_commit && start_commit == actual_end_commit
        raise <<-EOS.undent
          brew update didn't update master!
          Start commit:        #{start_commit}
          Expected end commit: #{end_commit}
          Actual end commit:   #{actual_end_commit}
        EOS
      end
    end
  end
end