…`Item`

deriving from `PyobjMixin`

closes #2137

…rdance to PEP-479

Fix #2160

Replace 'raise StopIteration' usages in the code by 'return's in accordance to PEP-479

See #2231 for discussion.

…lobals

'xfail' markers without a condition no longer rely on the underlying `Item` objects deriving from `PyobjMixin`

Do not asssume `Item.obj` in 'skipping' plugin

KeyboardInterrupt is a subclass of BaseException, but not of Exception.
Hence if we remove this except, KeyboardInterrupts will still be raised
so the behavior stays the same.

Descriptors (e.g. properties) such as in the added test case are
triggered during collection, executing arbitrary code which can raise.
Previously, such exceptions were propagated and failed the collection.
Now these exceptions are caught and the corresponding attributes are
silently ignored.

A better solution would be to completely skip access to all custom
descriptors, such that the offending code doesn't even trigger. However
I think this requires manually going through the instance and all of its
MRO for each and every attribute checking if it might be a proper
fixture before accessing it. So I took the easy route here.

In other words, putting something like this in your test class is still
a bad idea...:

    @Property
    def innocent(self):
        os.system('rm -rf /')

Fixes #2234.

ignore property errors when parsing fixure factories

…active

Allow to skip unittests if --pdb active

…"python_files"

#2238

Mention next training event.

As discussed in #2246

Improve pytest_plugins docs

--override-ini now correctly overrides some fundamental options like "python_files"

Python 3.6 invalid escape sequence deprecation fixes

Spelling fixes

Document pytest_report_header and conftest behavior

Simplify travis.yml with tox environment variables

In the xml report we now have two occurences for the system-out tag if
the testcase writes to stdout both on call and teardown and fails in
teardown.
This behaviour is against the xsd.
This patch makes sure that the system-out section exists only
once per testcase.

junitxml: Fix double system-out tags per testcase

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