Back in e3c6f240fd Junio taught
git-fetch to avoid copying objects when we are fetching from
a repository that is already registered as an alternate object
database. In such a case there is no reason to copy any objects
as we can already obtain them through the alternate.
However we need to ensure the objects are all reachable, so we
run `git rev-list --objects $theirs --not --all` to verify this.
If any object is missing or unreadable then we need to fetch/copy
the objects from the remote. When a missing object is detected
the git-rev-list process will exit with a non-zero exit status,
making this condition quite easy to detect.
Although git-fetch is currently a builtin (and so is rev-list)
we cannot invoke the traverse_objects() API at this point in the
transport code. The object walker within traverse_objects() calls
die() as soon as it finds an object it cannot read. If that happens
we want to resume the fetch process by calling do_fetch_pack().
To get around this we spawn git-rev-list into a background process
to prevent a die() from killing the foreground fetch process,
thus allowing the fetch process to resume into do_fetch_pack()
if copying is necessary.
We aren't interested in the output of rev-list (a list of SHA-1
object names that are reachable) or its errors (a "spurious" error
about an object not being found as we need to copy it) so we redirect
both stdout and stderr to /dev/null.
We run this git-rev-list based check before any fetch as we may
already have the necessary objects local from a prior fetch. If we
don't then its very likely the first $theirs object listed on the
command line won't exist locally and git-rev-list will die very
quickly, allowing us to start the network transfer. This test even
on remote URLs may save bandwidth if someone runs `git pull origin`,
sees a merge conflict, resets out, then redoes the same pull just
a short time later. If the remote hasn't changed between the two
pulls and the local repository hasn't had git-gc run in it then
there is probably no need to perform network transfer as all of
the objects are local.
Documentation for the new quickfetch function was suggested and
written by Junio, based on his original comment in git-fetch.sh.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Core GIT Tests
==============
This directory holds many test scripts for core GIT tools. The
first part of this short document describes how to run the tests
and read their output.
When fixing the tools or adding enhancements, you are strongly
encouraged to add tests in this directory to cover what you are
trying to fix or enhance. The later part of this short document
describes how your test scripts should be organized.
Running Tests
-------------
The easiest way to run tests is to say "make". This runs all
the tests.
*** t0000-basic.sh ***
* ok 1: .git/objects should be empty after git-init in an empty repo.
* ok 2: .git/objects should have 256 subdirectories.
* ok 3: git-update-index without --add should fail adding.
...
* ok 23: no diff after checkout and git-update-index --refresh.
* passed all 23 test(s)
*** t0100-environment-names.sh ***
* ok 1: using old names should issue warnings.
* ok 2: using old names but having new names should not issue warnings.
...
Or you can run each test individually from command line, like
this:
$ sh ./t3001-ls-files-killed.sh
* ok 1: git-update-index --add to add various paths.
* ok 2: git-ls-files -k to show killed files.
* ok 3: validate git-ls-files -k output.
* passed all 3 test(s)
You can pass --verbose (or -v), --debug (or -d), and --immediate
(or -i) command line argument to the test.
--verbose::
This makes the test more verbose. Specifically, the
command being run and their output if any are also
output.
--debug::
This may help the person who is developing a new test.
It causes the command defined with test_debug to run.
--immediate::
This causes the test to immediately exit upon the first
failed test.
Naming Tests
------------
The test files are named as:
tNNNN-commandname-details.sh
where N is a decimal digit.
First digit tells the family:
0 - the absolute basics and global stuff
1 - the basic commands concerning database
2 - the basic commands concerning the working tree
3 - the other basic commands (e.g. ls-files)
4 - the diff commands
5 - the pull and exporting commands
6 - the revision tree commands (even e.g. merge-base)
7 - the porcelainish commands concerning the working tree
8 - the porcelainish commands concerning forensics
9 - the git tools
Second digit tells the particular command we are testing.
Third digit (optionally) tells the particular switch or group of switches
we are testing.
If you create files under t/ directory (i.e. here) that is not
the top-level test script, never name the file to match the above
pattern. The Makefile here considers all such files as the
top-level test script and tries to run all of them. A care is
especially needed if you are creating a common test library
file, similar to test-lib.sh, because such a library file may
not be suitable for standalone execution.
Writing Tests
-------------
The test script is written as a shell script. It should start
with the standard "#!/bin/sh" with copyright notices, and an
assignment to variable 'test_description', like this:
#!/bin/sh
#
# Copyright (c) 2005 Junio C Hamano
#
test_description='xxx test (option --frotz)
This test registers the following structure in the cache
and tries to run git-ls-files with option --frotz.'
Source 'test-lib.sh'
--------------------
After assigning test_description, the test script should source
test-lib.sh like this:
. ./test-lib.sh
This test harness library does the following things:
- If the script is invoked with command line argument --help
(or -h), it shows the test_description and exits.
- Creates an empty test directory with an empty .git/objects
database and chdir(2) into it. This directory is 't/trash'
if you must know, but I do not think you care.
- Defines standard test helper functions for your scripts to
use. These functions are designed to make all scripts behave
consistently when command line arguments --verbose (or -v),
--debug (or -d), and --immediate (or -i) is given.
End with test_done
------------------
Your script will be a sequence of tests, using helper functions
from the test harness library. At the end of the script, call
'test_done'.
Test harness library
--------------------
There are a handful helper functions defined in the test harness
library for your script to use.
- test_expect_success <message> <script>
This takes two strings as parameter, and evaluates the
<script>. If it yields success, test is considered
successful. <message> should state what it is testing.
Example:
test_expect_success \
'git-write-tree should be able to write an empty tree.' \
'tree=$(git-write-tree)'
- test_expect_failure <message> <script>
This is the opposite of test_expect_success. If <script>
yields success, test is considered a failure.
Example:
test_expect_failure \
'git-update-index without --add should fail adding.' \
'git-update-index should-be-empty'
- test_debug <script>
This takes a single argument, <script>, and evaluates it only
when the test script is started with --debug command line
argument. This is primarily meant for use during the
development of a new test script.
- test_done
Your test script must have test_done at the end. Its purpose
is to summarize successes and failures in the test script and
exit with an appropriate error code.
Tips for Writing Tests
----------------------
As with any programming projects, existing programs are the best
source of the information. However, do _not_ emulate
t0000-basic.sh when writing your tests. The test is special in
that it tries to validate the very core of GIT. For example, it
knows that there will be 256 subdirectories under .git/objects/,
and it knows that the object ID of an empty tree is a certain
40-byte string. This is deliberately done so in t0000-basic.sh
because the things the very basic core test tries to achieve is
to serve as a basis for people who are changing the GIT internal
drastically. For these people, after making certain changes,
not seeing failures from the basic test _is_ a failure. And
such drastic changes to the core GIT that even changes these
otherwise supposedly stable object IDs should be accompanied by
an update to t0000-basic.sh.
However, other tests that simply rely on basic parts of the core
GIT working properly should not have that level of intimate
knowledge of the core GIT internals. If all the test scripts
hardcoded the object IDs like t0000-basic.sh does, that defeats
the purpose of t0000-basic.sh, which is to isolate that level of
validation in one place. Your test also ends up needing
updating when such a change to the internal happens, so do _not_
do it and leave the low level of validation to t0000-basic.sh.
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