On 10/03/14 16:04, Clark Boylan wrote:
On Mon, Mar 10, 2014 at 11:31 AM, Zane Bitter <zbit...@redhat.com> wrote:
Thanks Clark for this great write-up. However, I think the solution to the
problem in question is richer commands and better output formatting, not
discarding information.
On 07/03/14 16:30, Clark Boylan wrote:
But running tests in parallel introduces some fun problems. Like where
do you send logging and stdout output. If you send it to the console
it will be interleaved and essentially useless. The solution to this
problem (for which I am probably to blame) is to have each test
collect the logging, stdout, and stderr associated to that test and
attach it to that tests subunit reporting. This way you get all of the
output associated with a single test attached to that test and don't
have crazy interleaving that needs to be demuxed. The capturing of
This is not really a problem unique to parallel test runners. Printing to
the console is just not a great way to handle stdout/stderr in general
because it messes up the output of the test runner, and nose does exactly
the same thing as testr in collecting them - except that nose combines
messages from the 3 sources and prints the output for human consumption,
rather than in separate groups surrounded by lots of {{{random braces}}}.
Except nose can make them all the same file descriptor and let
everything multiplex together. Nose isn't demuxing arbitrary numbers
of file descriptors from arbitrary numbers of processes.
Can't each subunit process do the same thing?
As a user, here's how I want it to work:
- Each subunit process works like nose - multiplexing the various
streams of output together and associating it with a particular test -
except that nothing is written to the console but instead returned to
testr in subunit format.
- testr reads the subunit data and saves it to the test repository.
- testr prints a report to the console based on the data it just
received/saved.
How it actually seems to work:
- A magic pixie creates a TestCase class with a magic incantation to
capture your stdout/stderr/logging without breaking other test runners.
- Or they don't! You're hosed. The magic incantation is undocumented.
- You change all of your TestCases to inherit from the class with the
magic pixie dust.
- Each subunit process associates the various streams of output (if
you set it up to) with a particular test, but keeps them separate so
that if you want to figure out the order of events you have to direct
them all to the same channel - which, in practice, means you can only
use logging (since some of the events you are interested in probably
already exist in the code as logs).
- when you want to debug a test, you have to all the tedious loigging
setup if it doesn't already exist in the file. It probably won't,
because flake8 would have made you delete it unless it's being used already.
- testr reads the subunit data and saves it to the test repository.
- testr prints a report to the console based on the data it just
received/saved, though parts of it look like a raw data dump.
While there may be practical reasons why it currently works like the
latter, I would submit that there is no technical reason it could not
work like the former. In particular, there is nothing about the concept
of running the tests in parallel that would prevent it, just as there is
nothing about what nose does that would prevent two copies of nose from
running at the same time on different sets of tests.
this data is toggleable in the test suite using environment variables
and is off by default so that when you are not using testr you don't
get this behavior [0]. However we seem to have neglected log capture
toggles.
Oh wow, there is actually a way to get the stdout and stderr? Fantastic! Why
on earth are these disabled?
See above, testr has to deal with multiple writers to stdout and
stderr, you really don't want them all going to the same place when
using testr (which is why stdout and stderr are captured when running
testr but not otherwise).
Ah, OK, I think I understand now. testr passes the environment variables
automatically, so you only have to know the magic incantation at the
time you're writing the test, not when you're running it.
Please, please, please don't turn off the logging too. That's the only tool
left for debugging now that stdout goes into a black hole.
Logging goes into the same "black hole" today, I am suggesting that we
make this toggleable like we have made stdout and stderr capturing
toggleable. FWIW this isn't a black hole it is all captured on disk
and you can refer back to it at any time (the UI around doing this
could definitely be better though).
Hmm, now that you mention it, I remember Clint did the setup work in
Heat to get the logging working. So maybe we have to do the same for
stdout and stderr. At the moment they really do go into a black hole -
we can't see them in the testr output at all and nor are they stored in
the repository on disk.
It just seems bizarre to me that the _tests_ have to figure out what
test runner they are being run by and redirect their output to the
correct location to oblige it. Surely the point of a test runner is to
do the Right Thing(TM) for any test, regardless of what it knows about
the test runner.
BTW, since I'm on the subject, testr would be a lot more
confidence-inspiring if running `testr failing` immediately after running
`testr` reported the same number of failures, or indeed if running `testr`
twice in a row was guaranteed to report the same number of failures
(assuming that the tests themselves are deterministic). I can't imagine why
one of the subunit processes reporting a test failure is considered a
failure in itself (that's what it's supposed to do!), particularly when
`testr failing` manages to filter them out OK.
IIRC the test runner exiting non zero is a failure in itself to handle
cases where test runners die a horrible death without outputting any
failed subunit data. It could probably be cleaner but this way it is
preserved in the subunit log.
It makes sense for the case where the test runner has died without
reporting data, but why should it be reported as a separate failure when
it has reported data that testr has regarded as valid enough to use and
display?
My machine has 4 cores with hyperthreads (a common configuration, I
would imagine), so I have to do this mental translation every time:
1 failure -> everything failed
2 failures -> 1 failure
3 failures -> 2 failures
4 failures -> 2-3 failures
5 failures -> 3-4 failures
6 failures -> 3-5 failures
7 failures -> 4-6 failures
8 failures -> 4-7 failures
9 failures -> 5-8 failures
10 failures -> 5-9 failures
11 failures -> 6-10 failures
12 failures -> 6-11 failures
13 failures -> 7-12 failures
14 failures -> 7-13 failures
15 failures -> 8-14 failures
16 failures -> 8-15 failures
17 failures -> 9-16 failures
18 failures -> 10-17 failures
n>18 failures -> (n-8)-(n-1) failures
This means that the change statistic that testr prints is completely
useless for determining what I really needed to know, which is whether
the thing I just modified fixed any tests or not (or, alternatively,
whether I have an unstable test). For low-ish numbers of test failures
(say <15), it's dominated by random noise. Call me old-fashioned, but
random noise is not the distribution I'm looking for in reports from my
test runner :p
(I understand that some of the things mentioned above may already have been
improved since the latest 0.0.18 release. I can't actually find the repo at
the moment to check, because it's not linked from PyPI or Launchpad and
'testrepository' turns out to be an extremely common name for things on the
Internet.)
https://launchpad.net/testrepository is linked from pypi....
Ah, thanks. I looked at that page, but in my head I thought I had once
seen a Git repo for it and I couldn't see a link from there... I never
guessed that the upstream was in Launchpad's bzr.
cheers,
Zane.
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