t/README: Document the do's and don'ts of tests

[git] / t / README

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 3 subdirectories.
    ok 3 - success is reported like this
    ...
    ok 43 - very long name in the index handled sanely
    # fixed 1 known breakage(s)
    # still have 1 known breakage(s)
    # passed all remaining 42 test(s)
    1..43
    *** t0001-init.sh ***
    ok 1 - plain
    ok 2 - plain with GIT_WORK_TREE
    ok 3 - plain bare

Since the tests all output TAP (see http://testanything.org) they can
be run with any TAP harness. Here's an example of parallel testing
powered by a recent version of prove(1):

    $ prove --timer --jobs 15 ./t[0-9]*.sh
    [19:17:33] ./t0005-signals.sh ................................... ok       36 ms
    [19:17:33] ./t0022-crlf-rename.sh ............................... ok       69 ms
    [19:17:33] ./t0024-crlf-archive.sh .............................. ok      154 ms
    [19:17:33] ./t0004-unwritable.sh ................................ ok      289 ms
    [19:17:33] ./t0002-gitfile.sh ................................... ok      480 ms
    ===(     102;0  25/?  6/?  5/?  16/?  1/?  4/?  2/?  1/?  3/?  1... )===

prove and other harnesses come with a lot of useful options. The
--state option in particular is very useful:

    # Repeat until no more failures
    $ prove -j 15 --state=failed,save ./t[0-9]*.sh

You can also run each test individually from command line, like this:

    $ sh ./t3010-ls-files-killed-modified.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.
    ok 4 - git ls-files -m to show modified files.
    ok 5 - validate git ls-files -m output.
    # passed all 5 test(s)
    1..5

You can pass --verbose (or -v), --debug (or -d), and --immediate
(or -i) command line argument to the test, or by setting GIT_TEST_OPTS
appropriately before running "make".

--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.

--long-tests::
        This causes additional long-running tests to be run (where
        available), for more exhaustive testing.

--valgrind::
        Execute all Git binaries with valgrind and exit with status
        126 on errors (just like regular tests, this will only stop
        the test script when running under -i).  Valgrind errors
        go to stderr, so you might want to pass the -v option, too.

        Since it makes no sense to run the tests with --valgrind and
        not see any output, this option implies --verbose.  For
        convenience, it also implies --tee.

--tee::
        In addition to printing the test output to the terminal,
        write it to files named 't/test-results/$TEST_NAME.out'.
        As the names depend on the tests' file names, it is safe to
        run the tests with this option in parallel.

--with-dashes::
        By default tests are run without dashed forms of
        commands (like git-commit) in the PATH (it only uses
        wrappers from ../bin-wrappers).  Use this option to include
        the build directory (..) in the PATH, which contains all
        the dashed forms of commands.  This option is currently
        implied by other options like --valgrind and
        GIT_TEST_INSTALLED.

--root=<directory>::
        Create "trash" directories used to store all temporary data during
        testing under <directory>, instead of the t/ directory.
        Using this option with a RAM-based filesystem (such as tmpfs)
        can massively speed up the test suite.

You can also set the GIT_TEST_INSTALLED environment variable to
the bindir of an existing git installation to test that installation.
You still need to have built this git sandbox, from which various
test-* support programs, templates, and perl libraries are used.
If your installed git is incomplete, it will silently test parts of
your built version instead.

When using GIT_TEST_INSTALLED, you can also set GIT_TEST_EXEC_PATH to
override the location of the dashed-form subcommands (what
GIT_EXEC_PATH would be used for during normal operation).
GIT_TEST_EXEC_PATH defaults to `$GIT_TEST_INSTALLED/git --exec-path`.


Skipping Tests
--------------

In some environments, certain tests have no way of succeeding
due to platform limitation, such as lack of 'unzip' program, or
filesystem that do not allow arbitrary sequence of non-NUL bytes
as pathnames.

You should be able to say something like

    $ GIT_SKIP_TESTS=t9200.8 sh ./t9200-git-cvsexport-commit.sh

and even:

    $ GIT_SKIP_TESTS='t[0-4]??? t91?? t9200.8' make

to omit such tests.  The value of the environment variable is a
SP separated list of patterns that tells which tests to skip,
and either can match the "t[0-9]{4}" part to skip the whole
test, or t[0-9]{4} followed by ".$number" to say which
particular test to skip.

Note that some tests in the existing test suite rely on previous
test item, so you cannot arbitrarily disable one and expect the
remainder of test to check what the test originally was intended
to check.


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
   directory.$test_name_without_dotsh', with t/ subject to change by
   the --root option documented above.

 - 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.

Do's, don'ts & things to keep in mind
-------------------------------------

Here's a few examples of things you probably should and shouldn't do
when writing tests.

Do:

 - Put as much code as possible inside test_expect_success and other
   assertions.

   Even code that isn't a test per se, but merely some setup code
   should be inside a test assertion if at all possible. Test scripts
   should only have trivial code outside of their assertions.

 - Chain your test assertions

   Write test code like this:

        git merge foo &&
        git push bar &&
        test ...

   Instead of:

        git merge hla
        git push gh
        test ...

   That way all of the commands in your tests will succeed or fail. If
   you must ignore the return value of something (e.g. the return
   value of export is unportable) it's best to indicate so explicitly
   with a semicolon:

        export HLAGH;
        git merge hla &&
        git push gh &&
        test ...

Don't:

 - exit() within a <script> part.

   The harness will catch this as a programming error of the test.
   Use test_done instead if you need to stop the tests early (see
   "Skipping tests" below).

 - Break the TAP output

   The raw output from your test might be interpreted by a TAP
   harness. You usually don't have to worry about that. TAP harnesses
   will ignore everything they don't know about, but don't step on
   their toes in these areas:

   - Don't print lines like "$x..$y" where $x and $y are integers.

   - Don't print lines that begin with "ok" or "not ok".

   A TAP harness expect a line that begins with either "ok" and "not
   ok" to signal a test passed or failed (and our harness already
   produces such lines), so your script shouldn't emit such lines to
   their output.

   You can glean some further possible issues from the TAP grammar
   (see http://search.cpan.org/perldoc?TAP::Parser::Grammar#TAP_Grammar)
   but the best indication is to just run the tests with prove(1),
   it'll complain if anything is amiss.

Keep in mind:

 - That what you print to stderr and stdout is usually ignored

   Inside <script> part, the standard output and standard error
   streams are discarded, and the test harness only reports "ok" or
   "not ok" to the end user running the tests. Under --verbose, they
   are shown to help debugging the tests.


Skipping tests
--------------

If you need to skip all the remaining tests you should set skip_all
and immediately call test_done. The string you give to skip_all will
be used as an explanation for why the test was skipped. for instance:

        if ! test_have_prereq PERL
        then
            skip_all='skipping perl interface tests, perl not available'
            test_done
        fi

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 [<prereq>] <message> <script>

   Usually 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)'

   If you supply three parameters the first will be taken to be a
   prerequisite, see the test_set_prereq and test_have_prereq
   documentation below:

        test_expect_success TTY 'git --paginate rev-list uses a pager' \
            ' ... '

 - test_expect_failure [<prereq>] <message> <script>

   This is NOT the opposite of test_expect_success, but is used
   to mark a test that demonstrates a known breakage.  Unlike
   the usual test_expect_success tests, which say "ok" on
   success and "FAIL" on failure, this will say "FIXED" on
   success and "still broken" on failure.  Failures from these
   tests won't cause -i (immediate) to stop.

   Like test_expect_success this function can optionally use a three
   argument invocation with a prerequisite as the first argument.

 - test_expect_code [<prereq>] <code> <message> <script>

   Analogous to test_expect_success, but pass the test if it exits
   with a given exit <code>

 test_expect_code 1 'Merge with d/f conflicts' 'git merge "merge msg" B master'

 - 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.

 - test_tick

   Make commit and tag names consistent by setting the author and
   committer times to defined stated.  Subsequent calls will
   advance the times by a fixed amount.

 - test_commit <message> [<filename> [<contents>]]

   Creates a commit with the given message, committing the given
   file with the given contents (default for both is to reuse the
   message string), and adds a tag (again reusing the message
   string as name).  Calls test_tick to make the SHA-1s
   reproducible.

 - test_merge <message> <commit-or-tag>

   Merges the given rev using the given message.  Like test_commit,
   creates a tag and calls test_tick before committing.

 - test_set_prereq SOME_PREREQ

   Set a test prerequisite to be used later with test_have_prereq. The
   test-lib will set some prerequisites for you, e.g. PERL and PYTHON
   which are derived from ./GIT-BUILD-OPTIONS (grep test_set_prereq
   test-lib.sh for more). Others you can set yourself and use later
   with either test_have_prereq directly, or the three argument
   invocation of test_expect_success and test_expect_failure.

 - test_have_prereq SOME PREREQ

   Check if we have a prerequisite previously set with
   test_set_prereq. The most common use of this directly is to skip
   all the tests if we don't have some essential prerequisite:

        if ! test_have_prereq PERL
        then
            skip_all='skipping perl interface tests, perl not available'
            test_done
        fi

 - test_external [<prereq>] <message> <external> <script>

   Execute a <script> with an <external> interpreter (like perl). This
   was added for tests like t9700-perl-git.sh which do most of their
   work in an external test script.

        test_external \
            'GitwebCache::*FileCache*' \
            "$PERL_PATH" "$TEST_DIRECTORY"/t9503/test_cache_interface.pl

   If the test is outputting its own TAP you should set the
   test_external_has_tap variable somewhere before calling the first
   test_external* function. See t9700-perl-git.sh for an example.

        # The external test will outputs its own plan
        test_external_has_tap=1

 - test_external_without_stderr [<prereq>] <message> <external> <script>

   Like test_external but fail if there's any output on stderr,
   instead of checking the exit code.

        test_external_without_stderr \
            'Perl API' \
            "$PERL_PATH" "$TEST_DIRECTORY"/t9700/test.pl


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.