reftable/stack_test.c exercises the functions defined in
reftable/stack.{c, h}. Migrate reftable/stack_test.c to the
unit testing framework. Migration involves refactoring the tests
to use the unit testing framework instead of reftable's test
framework and renaming the tests to be in-line with unit-tests'
standards.

Since some of the tests use set_test_hash() defined by
reftable/test_framework.{c, h} but these files are not
'#included' in the test file, copy this function in the
ported test file.

With the migration of stack test to the unit-tests framework,
"test-tool reftable" becomes a no-op. Hence, get rid of everything
that uses "test-tool reftable" alongside everything that is used
to implement it.

While at it, alphabetically sort the cmds[] list in
helper/test-tool.c by moving the entry for "dump-reftable".

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Harmonize the newly ported test unit-tests/t-reftable-stack.c
with the following guidelines:
- Single line 'for' statements must omit curly braces.
- Structs must be 0-initialized with '= { 0 }' instead of '= { NULL }'.
- Array sizes and indices should preferably be of type 'size_t' and
  not 'int'.
- Function pointers should be passed as 'func' and not '&func'.

While at it, remove initialization for those variables that are
re-used multiple times, like loop variables.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Git's tempfile API defined by $GIT_DIR/tempfile.{c,h} provides
a unified interface for tempfile operations. Since reftable/stack.c
uses this API for all its tempfile needs instead of raw functions
like mkstemp(), make the ported stack test strictly use Git's
tempfile API as well.

A bigger benefit is the fact that we know to clean up the tempfile
in case the test fails because it gets registered and pruned via a
signal handler.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

In the current stack tests, ref records are compared for equality
by sometimes using the dedicated function for ref-record comparison,
reftable_ref_record_equal(), and sometimes by explicity comparing
contents of the ref records.

The latter method is undesired because there can exist unequal ref
records with some of the contents being equal. Replace the latter
instances of ref-record comparison with the former. This has the
added benefit of preserving uniformity throughout the test file.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

In a recent codebase update (commit ae8e378, merge branch
'ps/reftable-write-options', 2024/05/13) the geometric factor used
in auto-compaction of reftable tables was made configurable. Add
a test to verify the functionality introduced by this update.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

reftable_stack_init_ref_iterator and reftable_stack_init_log_iterator
as defined by reftable/stack.{c,h} initialize a stack iterator to
iterate over the ref and log records in a reftable stack respectively.
Since these functions are not exercised by any of the existing tests,
add a test for them.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>