Peer Review

Peer review is a process in which code changes are submitted to a staging environment, so that fellow developers have the opportunity to review the work before the code changes are submitted back to the source code management repository.

Peer view is assisted by Differential. To use Differential effectively, you must install arcanist and set it up.

For structured contributions, and for sprint participants, the use of Differential is obligatory, and further facilitates the process of Test-Driven Development.

Post-poning destabilizing changes stabilizes the day-to-day use of Winterfell, and allows multiple changesets to land at once (enabling a single feature to span multiple software projects).

The Process

A task in a sprint should consist of a bite-size chunk of development work.

When you start work on the task, you write the tests first (and those tests would fail, because they have not been backed by code changes).

You submit your differential at the earliest opportunity, however incomplete your coverage may be at that point. This ensures peers can participate in feedback cycles early, and shows progress being made as it is made.

Creating a Differential for Review

Your development takes place against the master branch, unless you find yourself running in circles, interrupted by a support request.

Thus, make sure you have master checked out, and for the sake of preventing superfluous merge and rebase exercises, ensure it’s in sync with upstream:

$ git checkout master
$ git fetch origin
$ git rebase origin/master --autostash

Provided a ticket, such as Task #1037, you should branch off the GIT repository;

[kanarip@dws06 docs.git (master u=)]$ git checkout -b dev/T1037
[kanarip@dws06 docs.git (dev/T1037)]$

This will allow you to keep your changes out of a tracking working copy, and allows you to switch back over to other work without stacking the changes on top of one another.

Make your changes, and commit them in however many commits you think is reasonable.

Then, create the Differential:

[kanarip@dws06 docs.git (dev/T1037 %)]$ arc diff
You have untracked files in this working copy.

  Working copy: /home/kanarip/devel/src/kolab/docs.git/

  Untracked changes in working copy:
  (To ignore these changes, add them to ".git/info/exclude".)

    Ignore these untracked files and continue? [y/N] y

You will now be requested to provide some information about your proposed changes.

The first line of the differential submission is the title for the differential.

The template offers a Summary: line, and you are to make that line include the phrase Resolves T1037. This causes the differential to be associated with the ticket, and will cause the ticket to change status to resolved when the differential is accepted, merged and pushed back.

Use the remainder of the space under Summary: Resolves T1037 to spout any thoughts or comments.

In Test Plan:, you list the steps needed to verify the work. This could be:

Test Plan: Run the unittests with;

  $ NOSE_VERBOSE=2 nosetests tests/unit/

In Reviewers:, you list the development team associated with the project (such as PyKolab Developers or Documentation Authors). You are to use hashtags here, so they would be #pykolab_developers or #documentation_authors. arcanist will validate the entries and prompt you if they do not exist.

In Subscribers:, you may either not list anyone, or list the username(s) of people you wish to be notified when the differential changes. Here too, arcanist validates the input.

No lint engine configured for this project.
Running unit tests...
No unit test engine is configured for this project.
Updating commit message...
Created a new Differential revision:
        Revision URI:

Included changes:
  M       source/index.rst
  A       source/contributor-guide/index.rst

Review Process

A reviewer must ensure code changes are verifiable, and validate unit, functional and integration tests for the code changes before accepting the differential.

A reviewer will want these tests to be automated, or ends up spending a lot of time and effort on verifying the changes made.


Exceptions to this rule should only be made in extreme cases, and require even more pairs of eyeballs.

A reviewer must also verify there is a ticket associated with the differential, and that the ticket associated with the differential will be closed automatically, should the differential be accepted and merged.

Accepting the differential does not mean the code changes are automatically merged, however. Acceptance of a differential outside of the merge window is therefore allowed.

Your changes need to be reviewed by at least one other person, who is a software development project member.

In Test-Driven Development, the submission of the differential associated with your review process aides in the staging of the code changes.

The changes submitted should be reviewed on Thursday afternoons at the latest, at which point of the Release Managers team can pick them up and merge the proposed changes with all the applicable branches.

The combined code changes and test should make the lives of Release Managers a lot easier – the functionality of the backported changes should be available for automated verification.

Landing a Differential Revision


This documentation applies to Release Managers only.

  1. Take the review column of the current sprint.

  2. Examine the tickets and their associated differentials.

  3. Move the tickets and differentials that have code changes depending on code changes to other projects that have not yet made it on to the next sprint, however, attempt to not negatively impact the team’s velocity in doing so;

    You could close the current ticket in review and move it to the Done column, and create a ticket for the next sprint associated with your own team, at about 1-2 story points.

  4. Merge the code changes in order of the differential numbers, in a best effort to merge stacked changes as easily as possible. Those that fail to be applied need to be merged manually, or otherwise reassigned to the developer in question for the next sprint (the task is rebase). Again, do not impact the team’s velocity too much, and consider splitting the original development effort with the rebase/merge attempt.

  5. Congratulate each developer on a job well done.

  6. Ensure merged code is available in Winterfell.

  7. Congratulate yourself on a job well done.