Re: [PATCH/RFC] branch: add tests for new copy branch feature

From: Junio C Hamano <gitster@pobox.com>
Date: May 29, 2017, 02:09 UTC
Message-ID: <xmqqr2z88lcy.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <0102015c5146c8ca-e5144538-326b-47b8-8c81-af31da4cdfe0-000000@eu-west-1.amazonses.com>

Sahil Dua <sahildua2305@gmail.com> writes:

> New feature - copying a branch along with its config section.

That's an unusual non-sentence (without a verb) in our commit message.

> Aim is to have an option -c for copying a branch just like -m option for
> renaming a branch.

What should it copy literally, and what should it copy with adjustment (and adjusting what), and what should it refrain from copying?

For example, when you create a branch topic-2 by copying from a branch topic-1, do you copy the reflog in such a way that topic-2's reflog contains all the entries of topic-1 before the copy happens, capped with a new (and not shared with topic-1) entry that says "Copied from topic-1"? When topic-1 is set to pull from a custom upstream 'upstream' (i.e. not "origin")'s 'trunk' branch, by setting 'branch.topic-2.remote' to "upstream", i.e. the same as the value of 'branch.topic-1.remote' and 'branch.topic-2.merge' to "trunk", i.e. the same as 'branch.topic-1.merge'? Should a "git push" while topic-2 is checked out push to the same remote as a "git push" would push to when topic-1 is checked out? Should they update the same branch at the remote? Why and/or why not? [*1*]

> This commit adds a few basic tests for getting any suggestions/feedback
> about expected behavior for this new feature.

Writing tests is a good way to prepare for an implementation, which must be done according to the design, but that happens after the design is polished and judged to be a good one. While soliciting comments on the design from others, tests are a bit too low level to express what you are aiming at. It is a bit unhelpful to those who may want to help to figure out answers to questions like the ones in the previos paragraph (the one that begins with "For example,...") by telling them to "read my intention from these tests", and when you want as wide an input as possible, that is counterproductive for your objective ;-).

Show 17 quoted lines

> Signed-off-by: Sahil Dua <sahildua2305@gmail.com>
> ---
>  t/t3200-branch.sh | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
>
> diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
> index fe62e7c775da..2c95ed6ebf3c 100755
> --- a/t/t3200-branch.sh
> +++ b/t/t3200-branch.sh
> @@ -341,6 +341,59 @@ test_expect_success 'config information was renamed, too' '
>  	test_must_fail git config branch.s/s/dummy
>  '
>  
> +test_expect_success 'git branch -c dumps usage' '
> +	test_expect_code 128 git branch -c 2>err &&
> +	test_i18ngrep "branch name required" err
> +'

OK. Do we want to support a single-name format (i.e. copy from the current)?

> +git config branch.d.dummy Hello

Write your tests to do as little outside test_expct_success block as possible, and do a set-up close to where it matters.

Show 7 quoted lines

> +test_expect_success 'git branch -c d e should work' '
> +	git branch -l d &&
> +	git reflog exists refs/heads/d &&
> +	git branch -c d e &&
> +	git reflog exists refs/heads/d &&
> +	git reflog exists refs/heads/e
> +'

A reasonable design of "copy" is for d's log to be left intact, and e's log to begin with a single entry "created by copying from d". Another possible design is to copy the log (making them identical), and then add one entry to e's log "created by copying from d".

The above test would succeed with either implementation and does not answer "should reflog be copied?" (see above about why "here are the tests that shows my thinking--read them and comment" is a bad approach).

"move" that makes the source of the movement disappear after the operation has a stronger justification of moving the log under the new name (the only alternative is to lose the history of the source forever), it is debatable if "copy" wants to retain a copy of the history of an otherwise unrelated branch, which has its own history retained after the operation.

Show 5 quoted lines

> +
> +test_expect_success 'config information was copied, too' '
> +	test $(git config branch.e.dummy) = Hello &&
> +	test $(git config branch.d.dummy) = Hello
> +'

The expectation is that a configuration like 'dummy' that does not have any meaning to Git itself will all blindly be copied, which is similar to what "move" does.

Show 9 quoted lines

> +git config branch.f/f.dummy Hello
> +
> +test_expect_success 'git branch -c f/f g/g should work' '
> +	git branch -l f/f &&
> +	git reflog exists refs/heads/f/f &&
> +	git branch -c f/f g/g &&
> +	git reflog exists refs/heads/f/f &&
> +	git reflog exists refs/heads/g/g
> +'

Hmph.  What's the reason to expect this not to work?

> +test_expect_success 'config information was copied, too' '
> +	test $(git config branch.f/f.dummy) = Hello &&
> +	test $(git config branch.g/g.dummy) = Hello
> +'

Isn't this part of the "should work" test above? The definition of working is not just reflog is created for the new branch without the old branch losing its reflog, right?

Show 6 quoted lines

> +test_expect_success 'git branch -c m2 m2 should work' '
> +	git branch -l m2 &&
> +	git reflog exists refs/heads/m2 &&
> +	git branch -c m2 m2 &&
> +	git reflog exists refs/heads/m2
> +'

Is it OK for the configuration be lost silently?

Thanks.

[Footnote]

*1* One way to avoid having to design an elaborate "definition of
    copying" from scratch is to piggy-back on whatever "move" does.
    Your definition of "copy" could be "copying from A to create B,
    followed by deleting A, should leave the identical result as
    moving A to create B".  And ask people if they agree with that
    definition as "the first principle".

    All the questions in the paragraph that begins with "For
    example..." and similar ones can be answered by followingthe
    first principle.