andrea kao 高沁蘭

brew log

2016-07-21

Google “brew log” and you’ll find many ways to log your homebrewing adventures, such as this page, from which the photo is taken.

Picking up where I left off (way back in this post)… here’s a discussion of the test coverage I added for brew log.

Like brew home, brew log can be run with or without arguments. When run without any arguments, brew log is akin to running git log on the Homebrew repository, i.e., it returns the commit history of the entire Git repository. When run with an argument in the form of a formula’s name, e.g., brew log ack, it returns the commit history for that formula.

My pull request for brew log proved more challenging than its 33 lines of code and existing 75% test coverage lead me to believe.

def test_log
  FileUtils.cd HOMEBREW_REPOSITORY do
    shutup do
      system "git", "init"
      system "git", "commit", "--allow-empty", "-m", "This is a test commit"
    end
  end
  assert_match "This is a test commit", cmd("log")
ensure
  (HOMEBREW_REPOSITORY/".git").rmtree
end

As shown above, the previously existing test does all these things:

• changes directory (FileUtils.cd) into the directory containing the Homebrew Git repository.
  • (from within this directory) calls shutup (defined in Homebrew/test/testing_env.rb) to shut up or suppress output from the commands that are enclosed between do and end:
    • calls system "git","init", which runs git init in a subshell:
      • git init initializes an empty Git repo by creating a /.git directory with various subdirectories and files.
    • calls system "git","commit", which runs git commit in a subshell:
      • git commit records a commit that includes no new changes from its parent commit (which is allowed when --allow-empty is passed), and uses the commit message, "This is a test commit".

• makes the assertion (with assert_match) that the recorded commit message is output when brew log is run.

• ensures (with ensure) the removal of the /.git directory at the end of the test.

In my pull request, I aimed to add coverage for the behavior that brew log exhibits when it’s called on a formula file or a shallow clone. My pull request broke a few things (oops) that were soon rectified by Martin’s follow-up PR (yay).

Here’s the incarnation of test_log_formula that emerged (and was soon updated again with the refactoring of the integration tests file):

  def test_log_formula
    core_tap = CoreTap.new
    formula_file = core_tap.formula_dir/"testball.rb"
    formula_file.write <<-EOS.undent
      class Testball < Formula
        url "https://example.com/testball-0.1.tar.gz"
      end
    EOS

    core_tap.path.cd do
      shutup do
        system "git", "init"
        system "git", "add", "--all"
        system "git", "commit", "-m", "This is a test commit for Testball"
      end
    end

    core_tap_url = "file://#{core_tap.path}"
    shallow_tap = Tap.fetch("homebrew", "shallow")
    shutup do
      system "git", "clone", "--depth=1", core_tap_url, shallow_tap.path
    end

    assert_match "This is a test commit for Testball",
                 cmd("log", "#{shallow_tap}/testball")
    assert_predicate shallow_tap.path/".git/shallow", :exist?,
                     "A shallow clone should have been created."
  ensure
    formula_file.unlink
    (core_tap.path/".git").rmtree
    shallow_tap.path.rmtree
  end
 

test_log_formula does these things:

• creates a testball.rb formula file in the Homebrew/homebrew-core tap.

• changes directory (core_tap.path.cd) into the directory containing the Homebrew/homebrew-core tap, which is /usr/local/Library/Taps/homebrew/homebrew-core.
  • (from within this directory) calls shutup and:
    • initializes an empty Git repo;
    • adds all new or modified files to the index, which holds a snapshot of the repo’s current content; and
    • records a commit and commit message.

• creates a core_tap_url variable and sets it equal to a string containing the file URI-formatted path to the Homebrew/homebrew-core tap.

• creates a shallow_tap variable and sets it equal to a newly instantiated Tap (named Homebrew/homebrew-shallow).

• calls shutup and:
  • makes a shallow Git clone (--depth=1) of the Homebrew/homebrew-core repo into the location where Homebrew/homebrew-shallow resides.

• makes a couple of assertions.

• ensures that all newly created files and directories are removed at the end of the test.

There you have it!