The reason is that with threading.Thread if exception happens in that
spawned thread, this error is not propagated to main driver, while with
sync.WorkGroup an exception from any spawned worker is propagated back
to main. For example with the following injected error

    --- a/nxdtest/__init__.py
    +++ b/nxdtest/__init__.py
    @@ -267,6 +267,7 @@ def main():

     # tee, similar to tee(1) utility, copies data from fin to fout appending them to buf.
     def tee(ctx, fin, fout, buf):
    +    1/0
         while 1:

before this patch nxdtest behaves like ...

    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ nxdtest
    date:   Tue, 24 Nov 2020 14:55:08 MSK
    xnode:  kirr@deco.navytux.spb.ru
    uname:  Linux deco 5.9.0-2-amd64 #1 SMP Debian 5.9.6-1 (2020-11-08) x86_64
    cpu:    Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz

    >>> pytest
    $ python -m pytest
    Exception in thread Thread-2:
    Traceback (most recent call last):
      File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
        self.run()
      File "/usr/lib/python2.7/threading.py", line 754, in run
        self.__target(*self.__args, **self.__kwargs)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero

    Exception in thread Thread-1:
    Traceback (most recent call last):
      File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
        self.run()
      File "/usr/lib/python2.7/threading.py", line 754, in run
        self.__target(*self.__args, **self.__kwargs)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero

    error   pytest  0.583s  # 1t 1e 0f 0s
    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ echo $?
    0

Here the error in another thread is only printed, but nxdtest is not aborted.
Above it reported "error", but e.g. when testing pygolang/py3 and raising an
error in tee it even reported it was succeeding
( nexedi/nxdtest!6 (comment 121393) ):

    slapuser34@vifibcloud-rapidspace-hosting-007:~/srv/runner/instance/slappart0$ ./bin/runTestSuite
    date:   Tue, 24 Nov 2020 12:51:23 MSK
    xnode:  slapuser34@vifibcloud-rapidspace-hosting-007
    uname:  Linux vifibcloud-rapidspace-hosting-007 4.19.0-6-amd64 #1 SMP Debian 4.19.67-2+deb10u2 (2019-11-11) x86_64
    cpu:    Intel(R) Xeon(R) CPU E5-2678 v3 @ 2.50GHz

    >>> thread
    $ python -m pytest
    Exception in thread Thread-1:
    Traceback (most recent call last):
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 926, in _bootstrap_inner
        self.run()
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 870, in run
        self._target(*self._args, **self._kwargs)
      File "/srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/nxdtest/nxdtest/__init__.py", line 268, in tee
        fout.write(data)
    TypeError: write() argument must be str, not bytes

    ok      thread  9.145s  # 1t 0e 0f 0s

    >>> gevent
    $ gpython -m pytest
    Exception in thread Thread-3:
    Traceback (most recent call last):
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 926, in _bootstrap_inner
        self.run()
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 870, in run
        self._target(*self._args, **self._kwargs)
      File "/srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/nxdtest/nxdtest/__init__.py", line 268, in tee
        fout.write(data)
    TypeError: write() argument must be str, not bytes

    ok      gevent  21.980s # 1t 0e 0f 0s

After this patch nxdtest correctly handles and propagates an error originating
in spawned thread back to main driver:

    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ nxdtest
    date:   Tue, 24 Nov 2020 14:54:19 MSK
    xnode:  kirr@deco.navytux.spb.ru
    uname:  Linux deco 5.9.0-2-amd64 #1 SMP Debian 5.9.6-1 (2020-11-08) x86_64
    cpu:    Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz

    >>> pytest
    $ python -m pytest
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/venv/z4-dev/bin/nxdtest", line 11, in <module>
        load_entry_point('nxdtest', 'console_scripts', 'nxdtest')()
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 230, in main
        wg.wait()
      File "golang/_sync.pyx", line 237, in golang._sync.PyWorkGroup.wait
        pyerr_reraise(pyerr)
      File "golang/_sync.pyx", line 217, in golang._sync.PyWorkGroup.go.pyrunf
        f(pywg._pyctx, *argv, **kw)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero
    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ echo $?
    1

NOTE sync.WorkGroup requires every worker to handle context cancellation, so
that whenever there is an error, all other workers are canceled. We add such
cancellation handling to tee but only lightly: before going to block in
read/write syscalls we check for whether ctx is canceled or not. However the
proper handling would be to switch file descriptors into non-block mode and to
select at every IO point on both potential IO events and potential
cancellation. This is left as TODO for the future.

/reviewed-on nexedi/nxdtest!7

These are the necessary changes to run `SlapOS.Eggs.UnitTest-*` and `SlapOS.SoftwareReleases.IntegrationTest-*` using nxdtest

See merge request nexedi/nxdtest!6

/reviewed-by @kirr

If test program output on stderr (which is unbuffered), the
output of the test program will appear before output from nxdtest
advertising the program that is about to be executed, because nxdtest
stdout is buffered (testnode does not set PYTHONUNBUFFERED, and eventhough
nxdtest sets PYTHONUNBUFFERED in its own environ, this only applies to sub
processes)

While pytest sends everything in stdout, some other programs send on stderr.

While treating output as text would not really be impossible, treating it
as bytes seems a better choice because:
 - we don't have to make assumptions about what output encoding the test
   program is using for output
 - `tee` can just read stream output bytes by bytes without having to worry
   about multi-bytes characters
 - testnode protocol uses xmlrpc.client.Binary, which uses bytes.

Because using bufsize=1 implies reading subprocess output as text, we use
bufsize=0 instead in the subprocess.Popen call, to prevent buffering.

To make manipulation of strings and bytes easier, we add a dependency on
pygolang, so that we can use its strings utility functions.

Also add a few tests to verify general functionality.

For example wendelin.core 2 uses pytest_unconfigure to unmount wcfs
servers that it spawned:

https://lab.nexedi.com/kirr/wendelin.core/blob/1be4d730/conftest.py#L27-53

This usually leads to some test as shown in added test.

-> Skip that text backwards and actually detect pytest summary line
instead of returning empty dict, because empty dict forces Nexedi ERP5
to treat such test run to have UNKNOWN status, e.g.

https://erp5.nexedi.net/test_result_module/20201108-C170850/11

/cc @jerome
/reviewed-on nexedi/nxdtest!5

This allows to establish tests for Nxdtest itself under Nexedi testing
infrastructure.

/cc @jerome
/reviewed-on nexedi/nxdtest!4

lab.nexedi.com/kirr/nxdtest -> lab.nexedi.com/nexedi/nxdtest

nexedi/slapos!839 (comment 119120)
nexedi/slapos!839 (comment 119142)

/cc @jerome
/reviewed-on nexedi/nxdtest!3

/cc @jerome
/reviewed-on nexedi/nxdtest!1

Verify pytest summary-parsing functionality.

Create real nxdtest module, so that things could be imported from there.
As the result switch `nxdtest` program from scripts to entry_point.

Here is e.g. corresponding summary:

    ===== 12 failed, 14 passed, 4 xfailed, 12 error in 19.58 seconds =====

When checking logs on testnode, it is very useful to know which kernel
version is running inside (wendelin.core uses FUSE and depends on having
patched FUSE module for kernels < 5.2), which CPU is there, etc.

Format of printed output follows go benchmarking format and coincides
with start of `neotest info-local` (see footers on figures in
http://navytux.spb.ru/~kirr/neo.html and here:
https://lab.nexedi.com/kirr/neo/blob/1f26678b/go/neo/t/neotest#L585-874)

- To list which tests are in there,
- To execute only selected tests.

Apply only to local mode.
Very handy for debugging.

We started to print test result summary line for a testcase run since
0153635b (Teach nxdtest to run tests locally). However it is not present
in log when nxdtest is run under master. -> Include summary lines
everywhere for uniformity, with reason similar to bd1333bb (log += title
and argv for ran testcase).

This reverts commit 34e96b1d. Reason for revert is that since bd1333bb
(log += title and argv for ran testcase) we always emit details of
to-be-run command to log in the beginning of testcase run.

We started to display command and envadj in the log in the previous
patch. However only command - without envadj - was reported to master
for test result. -> Make it uniform: include envadj into details
everywhere.

When there are several or many testcases, it is hard to understand - by
seeing just log or console output - which part of the test suite was
running. It also helps to see the exact command that was spawned.

Example output for pygolang. Before:

    (neo) (z-dev) (g.env) kirr@deco:~/src/tools/go/pygolang$ nxdtest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ssssss.sssssss                                   [100%]

    ==================== 99 passed, 13 skipped in 5.42 seconds =====================
    ok      thread  5.656s  # 112t 0e 0f 13s
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ..............                                   [100%]

    ========================= 112 passed in 17.35 seconds ==========================
    ok      gevent  17.768s # 112t 0e 0f 0s

After:

(neo) (z-dev) (g.env) kirr@deco:~/src/tools/go/pygolang$ nxdtest

    >>> thread
    $ python -m pytest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ssssss.sssssss                                   [100%]

    ==================== 99 passed, 13 skipped in 5.27 seconds =====================
    ok      thread  5.508s  # 112t 0e 0f 13s

    >>> gevent
    $ gpython -m pytest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ..............                                   [100%]

    ========================= 112 passed in 17.32 seconds ==========================
    ok      gevent  17.729s # 112t 0e 0f 0s

failure is assertion failure.
error is any other error.

Source: https://docs.python.org/3/library/unittest.html#organizing-test-code
-> "If the test fails, an exception will be raised ... identify the test
case as a failure. Any other exceptions will be treated as errors"

While searching ERP5 code for failure_count to clarify its meaning, I've
also discovered expected_failures and unexpected_successes (*) so they
are also added to the table.

(*) see e.g. https://lab.nexedi.com/nexedi/erp5/blob/1e31c091/product/ERP5Type/tests/ERP5TypeTestSuite.py#L6-8

Instead of just traceback saying that e.g. "No such command" without
information which command it was tried to spawn, stderr will now include
what was tried to be run. This makes diagnostic easier.

Many project that use pytest for testing won't need to redefine it over
and over again in their .nxdtest file.

It is very handy to debug both .nxdtest and nxdtest tool itself, and to
be able to run tests locally during development instead of (in addition
to) waiting for the test result from test nodes.

-> Teach nxdtest to run and report tests locally if no --master_url was
provided.

Idea is taken from runTestSuite.in from NEO, Cython+, Buildout and Rina:

https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/runTestSuite.in#L95-105
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/runTestSuite.in#L55-75
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/stress-testing/runTestSuite.in#L17-37
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/cython-test/runTestSuite.in#L38-58
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/buildout-testing/runTestSuite.in#L21-39
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/build-rina/runTestSuite.in#L29-49

Instead of copying code over and over again, let's stick to UNIX
approach and make it to be in one tool only that does its job
(hopefully) good.

Previously, if --master_url was not provided, the program would crash
with UnboundLocalError for status, since for that case list of tests was
empty. Fix it by moving status initialization higher by one level.

See next patch where we'll add meaning for nxdtest run with no
--master_url set.

It is frequently needed to set some environment variable without
completely resetting everything else in the environment, because that
everything else can carry settings like PATH, PYTHONPATH, RPATH, etc for
the program to be able to run at all.

See nexedi/pygolang@b938af8b for recent example.

After previous patch that summary function is no-longer used, is
specific to NEO/py and so should be defined in .nxdtest file in that
project. lab.nexedi.com/kirr/neo will be adjusted correspondingly.

Make the tool generic: load list of testcases to run from .nxdtest file
and process the correspondingly. See added top-level documentation for
details.

Amends e9cc7e07 (Add minimal packaging setup)

So that nxdtest could be installed as egg via pip or buildout.

We will use it as the base for nxdtest.
Original history:

neo@51b18490
neo@f67c147d
neo@0e28fbb8

We send output from tested process to master. We also print it to
stdout,stderr so it appears in testnode logs.

However till now it was like, whole output first read, and only then
emitted to log as a whole, thus not allowing to oversee current test
progress by watching testnode log tail.

Fix it by implementing the teeing process manually.

Some draft history related to this patch:

	lab.nexedi.com/kirr/neo/commit/aa370ca3        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/096550b1        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/63956f43        fixup! X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally
	lab.nexedi.com/kirr/neo/commit/b9819d0e        X neotest/runTestSuite: Tee tested process stdout,stderr to testnode logs incrementally

The wrapper runs `neotest bench-local` in neotest SlapOS instance:

	https://lab.nexedi.com/nexedi/slapos/blob/ab8705f4/software/neotest/instance.cfg.in

Extracted from slapos!282

Nxdtest is conceived as a tox-like tool to run tests for a project under
Nexedi testing infrastructure.