Re: [RFC][GSoC] Proposal v2: Move more tests to the unit testing framework

[Chandra Pratap <chandrapratap3519@gmail.com>]

Thanks for the feedback, Christian and Patrick! With your advice, I
decided to split my original proposal into two to conform to what was
suggested by the SoC 2024 Ideas page.
This is the proposal for the unit tests migration project.

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Personal Info
-------------

Full name: Chandra Pratap
Preferred name: Chand

E-mail: chandrapratap3519@gmail.com
Phone: (+91)77618-24030

Education: SV National Institute of Technology, Surat, India
Year: Sophomore (2nd)
Major: Mathematics

GitHub: https://github.com/Chand-ra

Before GSoC
-----------

-----Synopsis-----

A new unit testing framework was introduced to the Git mailing list last
year with the aim of simplifying testing and improving maintainability
by moving the current testing setup from shell scripts and helper files
to a framework written wholly in C. The idea was accepted and merged
into master on 09/11/2023. The choice of testing framework and the
reasoning behind the choice is described in
Documentation/technical/unit-tests.txt.

This project aims to extend that work by moving more tests from the current
setup to the new unit testing framework. The difficulty for the project
should be medium and it should take somewhat between 175 to 350 hours.

-----Contributions-----

• apply.c: make git apply respect core.fileMode settings
-> Status: merged into master
-> link: https://public-inbox.org/git/20231226233218.472054-1-gitster@pobox.com/
-> Merge commit: cf47fb7ec7e183a1a1e521a540862fba3c2a89eb

-> Description: When applying a patch that adds an executable file, git 
apply ignores the core.fileMode setting (core.fileMode specifies whether
the executable bit on files in the working tree are to be honored or not)
resulting in false warnings. Fix this by inferring the correct file mode 
from the existing index entry when core.filemode is set to false. Add a
test case that verifies the change and prevents future regression.

-> Remarks: This was the first patch I worked on as a contributor to Git.
Served me as an essential intro lesson to the community’s working flow and
general practices.

• tests: Move t0009-prio-queue.sh to the unit testing framework
-> Status: merged into master
-> link: https://public-inbox.org/git/pull.1642.v4.git.1705865326185.gitgitgadget@gmail.com/
-> Merge commit: 107023e1c9f981476c505e73eab319db6534a536

-> Description: t/t0009-prio-queue.sh along with t/helper/test-prio-queue.c
unit test Git's implementation of a priority queue. Migrate the test
over to the new unit testing framework to simplify debugging and reduce
test run-time.

-> Remarks: Probably the most relevant patch of all the ones mentioned
here, I decided to work on this patch well before I decided to take part
in this year’s GSoC. This patch helped me understand the expectations and
workflow for the work to be performed in unit tests migrations.

• write-or-die: make GIT_FLUSH a Boolean environment variable
-> Status: merged into master
-> link: https://public-inbox.org/git/pull.1628.v3.git.1704363617842.gitgitgadget@gmail.com/
-> Merge commit: b3049bbb97c9c0d0292bc9239e976cc661961f39

-> Description: Among Git's environment variables, the ones marked as
"Boolean" accept values like Boolean configuration variables, i.e. 
values like 'yes', 'on', 'true' and positive numbers are taken as "on"
and  values like 'no', 'off','false' are taken as "off". Make GIT_FLUSH 
accept more values besides '0' and '1' by turning it into a Boolean 
environment variable & update the related documentation.

• sideband.c: remoye redundant NEEDSWORK tag
-> Status: merged into master
-> link: https://public-inbox.org/git/pull.1625.v4.git.1703750460527.gitgitgadget@gmail.com/
-> Merge commit: 6484eb9a97fe3cd81a2d5711183b93494e6ddefa

-> Description: Replace a misleading NEEDSWORK tag in sideband.c that
reads ‘replace int with size_t’ with another comment explaining why it
is fine to use ‘int’ and the replacement isn’t necessary.

• make tig callable from PowerShell/Command Prompt
-> Status: merged into main (Git for Windows)
-> link: https://github.com/git-for-windows/MINGW-packages/pull/104
-> Merge commit: 8eb71eb31c6a1b5d41b253c1ab66d981cc448cb0

-> Description: Tig is a text mode interface for Git that ships with the
standard Git for Windows package but isn’t callable from PowerShell/
Command Prompt by default. Fix this by updating the relevant Makefiles
and resource scripts.

• fix broken link on Git for Windows’ GitHub wiki
-> Status: merged (Git for Windows)
-> link: https://github.com/git-for-windows/git/wiki/Home/_history
-> Merge commit: 0df663304bce986da6571cca48b34508d4823a11

-> Remarks: A simple fix for a broken link that I stumbled upon while
browsing Git for Windows’ wiki looking for some help with the patch 
mentioned just before this one.

• t4129: prevent loss of exit codes due to the use of pipes
-> Status: merged into master
-> link: https://public-inbox.org/git/pull.1636.git.1704891257544.gitgitgadget@gmail.com/
-> Merge commit: 1b095626937a858e3a68e9c7d1de11b71117bb42

-> Description: Piping the output of git commands like git-ls-files to
another command (grep in this case) in t4129 hides the exit code returned
by these commands. Prevent this by storing the output of git-ls-files to
a temporary file and then "grep-ping" from that file. Replace grep with
test_grep as the latter is more verbose when it fails.

• t9146: replace test -d/-f with appropriate test_path_is_* function
-> Status: merged into master
-> link: https://public-inbox.org/git/pull.1661.v3.git.1707933048210.gitgitgadget@gmail.com/
-> Merge commit: 90c0c15e56fa761ae8c4cf5f5fe09b329c0a5dc5

-> Description: The helper functions test_path_is_* provide better debugging
information than test -d/-e/-f.
Replace tests -d/-e/-f with their respective ‘test_path_is_foo’ calls.

• regex: update relevant files in compat/regex
-> Status: WIP (GitGitGadget PR)
-> link: https://github.com/gitgitgadget/git/pull/1641

-> Description: The RegEx code in compat/regex has been vendored from 
gawk and was last updated in 2010. This may lead to performance issues 
like high CPU usage. Fix this by synchronizing the relevant files in 
compat/regex with the latest version from GNULib and then replaying any
changes we made to gawk’s version on top of the new files.

-> Remarks: When I started working on this patch, I thought it was an
easy fix but the work turned out to be more involved than I anticipated.
I had to seek help from the other community members, and we have made
some good progress, but there is still a lot of cleaning and changes that
need to be done. I haven’t found enough time to commit to this again,
but it’s surely something that I want to get done soon.

• tests: Move t0032-reftable-unittest.sh to the unit testing framework
-> Status: WIP (GitGitGadget PR)
-> link: https://github.com/gitgitgadget/git/pull/1698

-> Description: t/t0032-reftable-unittest.sh along with t/helper/test-reftable.c
unit test Git’s reftable framework. Migrate the test over to the new
unit testing framework to simplify debugging and reduce test run-time.

-> Remarks: An infant version as of now, I tinkered with this after 
seeing the project list on 'Git SoC 2024 Ideas' page to get an idea of
the kind of work that will be involved in the ‘Move reftable tests to
the new unit testing framework’ project.

• commit.c: ensure find_header_mem() doesn't scan beyond given range
-> Status: Dropped

-> Remarks: This was a patch addressing a NEEDSWORK comment in commit.c
which was dropped because René Scharfe found out a better way to fix the
issue at hand than my approach or what the NEEDSWORK comment suggested.


-----Related Work-----

Prior works about the idea have been performed by other community members
and previous interns which form a good guiding path for my own approach.
Some previous example work:

i) Port helper/test-ctype.c to unit-tests/t-ctype.c
-> link: https://lore.kernel.org/git/20240112102743.1440-1-ach.lumap@gmail.com/

ii) Port test-sha256.c and test-sha1.c to unit-tests/t-hash.c
-> link: https://lore.kernel.org/git/20240229054004.3807-2-ach.lumap@gmail.com/

iii) Port helper/test-date.c to unit-tests/t-date.c
-> link: https://lore.kernel.org/git/20240205162506.1835-2-ach.lumap@gmail.com/

iv) Port test-strcmp-offset.c to unit-tests/t-strcmp-offset.c
-> link: https://lore.kernel.org/git/20240310144819.4379-1-ach.lumap@gmail.com/

v) Integrate a simple strbuf unit test with Git's Makefiles
-> link: https://lore.kernel.org/git/20230517-unit-tests-v2-v2-4-21b5b60f4b32@google.com/

vi) t0080: turn t-basic unit test into a helper
-> link: https://lore.kernel.org/git/a9f67ed703c8314f0f0507ffb83b503717b846b3.1705443632.git.steadmon@google.com/

In GSoC
-------

-----Plan-----

Tests for Git are defined in the t/ directory and use the combination of
a helper file (written in C) and a shell script that invokes the said
helper file. I will use my work from the patch ‘tests: Move
t0009-prio-queue.sh to the unit testing framework’ to explain the steps
involved in the porting of such tests:

• Search for a suitable test to port: 

As Christian Couder mentioned in this mail (link: https://public-inbox.org/git/CAP8UFD22EpdBU8HJqFM+=75EBABOTf5a0q+KsbzLK+XTEGSkPw@mail.gmail.com/),
there exists a subset of t/helper worth porting and we need some sort of
classification to discern these.

All helper files contain a cmd__foo() function which acts as the entry
point for that helper tool. For example, the helper/test-prio-queue.c
file contained cmd__prio_queue() which served as the entry point for
that file. The binary for the helper file is then mapped to a different
name by helper/test-tool.c which is used by the ‘*.sh’ files to perform
the tests. This name can be discovered by searching for the helper
file’s entry point in test-tool.c. Continuing the prior example,
“prio-queue” was the name for the helper/test-prio-queue.c binary and
t0009-prio-queue.sh invoked it like “prio-queue 1 2 get 3 dump”.

To classify what among t/helper should be targeted first in this
project, we can use something like ‘git grep foo’ (where foo is the name
for the helper’s binary) to look at the instances where the helper tool
is invoked. The ones appearing lesser in different test scripts are the
ones most likely to be used solely for unit testing and should probably
be targeted first. Utilising this strategy, I discovered that the
‘prio-queue’ tool was only used in t0009-prio-queue.sh and hence, was a
good candidate for the unit testing framework.
Note that this strategy is not full-proof and further investigation is
absolutely required on a per-test basis, it is only meant to give an
initial idea of what’s worth investigating.

•  Create a new C test file in t/unit-tests: 

After finding a test appropriate for the migration efforts, we create a
new ‘*.c’ file in t/unit-tests.  The test file must be named appropriately
to reflect the nature of the  tests it is supposed to perform.
Most of the times, replacing ‘tXXXX’  with ‘t-‘ and ‘*.sh’ with ‘.c’ in
the name of the test script suffices. E.g. t/t0009-prio-queue.sh turns
to t/unit-tests/t-prio-queue.c.
The new C file must #include “test-lib.h” (to be able to use the unit
testing framework) and other necessary headers files.

•  Move the code from the helper file: 

Since the helper files are written in C, this step is mostly a
‘copy-paste then rename’ job. Changes similar to the following also need
to be made in the Makefile:
-    TEST_BUILTINS_OBJS += test-prio-queue.o
+    UNIT_TEST_PROGRAMS += t-prio-queue

•  Translate the shell script: 

The trickiest part of the plan, since  different test scripts perform
various functions and a direct translation of the scripts to C is not
always optimal. Continuing the prior example, t0009-prio-queue.sh used a
single pattern for testing, write expected output to a temporary file
(named ‘expect’) -> feed input to the ‘prio-queue’ helper tool -> dump its
output to another temporary file (named ‘actual’) -> compare the two files
(‘actual’ vs ‘expect’).

In the first iteration of my prio-queue patch, I worked out a
straightforward translation of this pattern in C. I stored the input in
a string buffer, passed that buffer to the test function, stored its
output in another buffer and then called memcmp() on these two buffers.
While this did prove to be a working copy, this work was found to be inadequate
on the mailing list. Through the next several iterations, I reworked the
logic several times, like comparing the input and output on-the-go rather
than using buffers and replacing strings with macro definitions.

The test scripts similarly perform other functions like checking for
prerequisites, creating commits, initializing repositories, changing or 
creating directories and so forth, and custom logic is required in most
of the cases of translating these, as seen above.

•  Run the resulting test, correct any errors:

It is rare for any migrated test to work correctly on the first run.
This step involves resolving any compile/runtime errors arising from the
test and making sure that at the very minimum, all the test-cases of the
original test are replicated in the new work. Improvements upon the original
can also be made, for example, the original t0009-prio-queue.sh did not
exercise the reverse stack functionality of prio-queue, which I improved
upon in unit-tests/t-prio-queue.

•  Send the resulting patch to the mailing list, respond to the feedback:

This step involves writing a meaningful commit message explaining each patch
in the series. From my experience contributing to the Git project, I find it
to be rare for any patch series to be accepted in the very first iteration.
Feedback from the community is vital for the refinement of any patch and
must be addressed by performing the suggested changes and sending the work
back to the mailing list. This must be repeated until the work is merged
into ‘seen’, ‘next’ and further down, ‘master’.

Timeline
--------

I’m confident that I can start the project as early as the start of the
Community Bonding Period (May 1 - 26). This is because I have read
the related documentation and already have some experience with the idea.
I believe I’ll be ready to get up to speed to work on the project by then.
The exact time arrangement for each test is variable and hard to determine,
but judging from the fact that it took me 3-4 days to complete the first
iteration of the t-prio-queue work, here is a proposed migration schedule:

The first few steps of the plan are easy enough to knock out in a day,
the time required to port the tests depends mostly upon the work
required in translating the shell script. As mentioned previously, it
took me 3-4 days to complete the first iteration of the test-prio-queue
migration patch and that was a short test with only about 50 or so lines
of shell scripting and all the test cases following a single pattern.
Considering all this, I believe it should be possible, on average, to
migrate a new test in 4-7 days.
From there, it’s a matter of polishing the patch until integration with
‘master’ by addressing the feedback on the mailing list which can
deceptively take longer than expected. For instance, I had to continue
refining my t-prio-queue patch for around 2 weeks after the first
iteration to get it merged to ‘next’.

Hence, it should be possible for me to migrate >=8 tests throughout the
duration of this project.

Blogging
--------

I plan on writing weekly blogs on the weekends summarizing my work and
outlining future plans here (link: https://chand-ra.github.io/)
(I have yet to set up the blog). This is because I believe jotting ideas
down help you understand them better while simultaneously serving as a
guiding path for new contributors to get started with the Git project.
I learnt quite a lot from previous intern’s blogs like Shaoxuan Yuan’s
GSoC 2022 Blog (link: https://ffyuanda.github.io/), Shuqi Lang’s GSoC
2023 blog (link: https://cheskaqiqi.github.io/) and Achu Luma’s Outreachy
2023 Blog (link: https://gitlab.com/lumap/lumap.gitlab.io) and plan on
leaving something similar for other newcomers.

Availability
------------

My summertime is reserved for GSoC, so I expect that I can work on a new 
test 5 days per week, 6-8 hours per day, that is 30-40 hours a week.
On the weekends, I would like to solely work on the feedback from
the mailing list and advance my [WIP] patches. Certainly, something
unexpected may arise, but I will try my best to adhere to this time
commitment and be always available through the community’s mailing list.

Post GSoC & Closing Remarks
---------------------------

When I first started contributing to the Git project in October of 2023,
I had no idea about programmes like GSoC. I was advised by a senior of
mine to contribute to open-source projects and hence, my aim of contribution
was to apply what I had learnt in college to solve real-world problems
and learn from more experienced peers. However, most of what I have
contributed to Git has been trivial owing to my lack of skills and
inexperience with the project.

Seeing how I need to do an internship in summer, with GSoC, I hope to be
able to dedicate this internship time and effort to a cool project like
Git while simultaneously learning skills to be able to make more useful
contributions in the future. It’s two birds with one stone. I would also
like to keep working on this project to see it to completion post-GSoC
and help mentor other newcomers get started with the Git project.

Thanks & Regards,
Chandra