Re: debugging git tests, was: Re: [PATCH v4 2/8] t5520: test no merge candidates cases

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> On Mon, May 18, 2015 at 10:46:50AM -0700, Junio C Hamano wrote:
>
>> The test framework is aware of the fact that it needs to help the
>> people who are debugging the scripts.  The support is limited to the
>> case in which you run it under the -i option, i.e.
>> 
>> 	$ cd t
>>         $ sh ./t5520-pull.sh -i -v
>> 
>> will refrain from running test_when_finished scripts when the test
>> piece fails.  Even though this is only limited to -i, I found it
>> often sufficient for debugging.
>
> If you don't use "-i", you are pretty much screwed anyway, because the
> subsequent tests will stomp all over the state of the test directory.

Yeah.

> Many a head-scratching session has been caused by looking at the wrong
> state, and these days my go-to options for debugging a test are "-v -i".
> But since we are talking about it in a related thread, I will advertise
> the new "-x" here, too.  :)

Yes, thanks for "-x".  That has been very helpful.

> As a side note, I've also considered better support for running the
> debugger on git commands inside a test (right now, I usually stick a
> "gdb --args" in the pipeline, but you have to remember to run with "-v",
> and to redirect stdin appropriately). Do other people have this
> annoyance, too?

I usually tweak the script and have it stop before the offending
test, and then go through the steps in the test manually X-<.  If it
can be more automated, that would be great.

I haven't been ambitious enough to even attempt it so do not have
anything to add to the implementation ideas at this point.

> I'm vaguely thinking of something like putting debug support into
> bin-wrappers/git, but activating it only for certain tests (so you could
> say "t5520-pull.sh --gdb=10", and git would start under the debugger
> only for test 10). I think we'd also have to use gdbserver for I/O
> sanity, and maybe provide short script to do:
>
>    gdb -ex "target remote localhost:$some_port" "$TEST_DIRECTORY"/../git
>
> That still doesn't cover all cases (when git spawns an external command,
> you probably want to run the debugger on that; likewise, I have a
> git-remote-debug hack for debugging remote-curl). I suspect with clever
> use of gdb options that you could convince the original gdb invocation
> to end up tracing the process you care about, though.
>
> -Peff