Ignore errors raised from descriptors when collecting fixtures

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.

AUTHORS

@@ -118,6 +118,7 @@ Piotr Banaszkiewicz
 Punyashloka Biswal
 Quentin Pradet
 Ralf Schmitt
+Ran Benita
 Raphael Pierzina
 Raquel Alegre
 Roberto Polli

CHANGELOG.rst

@@ -3,6 +3,9 @@
 
 *
 
+* Ignore exceptions raised from descriptors (e.g. properties) during Python test collection (`#2234`_).
+  Thanks to `@bluetech`_.
+
 * Replace ``raise StopIteration`` usages in the code by simple ``returns`` to finish generators, in accordance to `PEP-479`_ (`#2160`_).
   Thanks `@tgoodlet`_ for the report and `@nicoddemus`_ for the PR.
 
@@ -16,6 +19,10 @@
 
 *
 
+.. _#2234: https://github.com/pytest-dev/pytest/issues/2234
+
+.. _@bluetech: https://github.com/bluetech
+
 .. _#2160: https://github.com/pytest-dev/pytest/issues/2160
 
 .. _PEP-479: https://www.python.org/dev/peps/pep-0479/

_pytest/fixtures.py

@@ -14,6 +14,7 @@ from _pytest.compat import (
     getfslineno, get_real_func,
     is_generator, isclass, getimfunc,
     getlocation, getfuncargnames,
+    safe_getattr,
 )
 
 def pytest_sessionstart(session):
@@ -1066,7 +1067,9 @@ class FixtureManager:
         self._holderobjseen.add(holderobj)
         autousenames = []
         for name in dir(holderobj):
-            obj = getattr(holderobj, name, None)
+            # The attribute can be an arbitrary descriptor, so the attribute
+            # access below can raise. safe_getatt() ignores such exceptions.
+            obj = safe_getattr(holderobj, name, None)
             # fixture functions have a pytest_funcarg__ prefix (pre-2.3 style)
             # or are "@pytest.fixture" marked
             marker = getfixturemarker(obj)

testing/python/collect.py

@@ -166,6 +166,16 @@ class TestClass:
             "because it has a __new__ constructor*"
         )
 
+    def test_issue2234_property(self, testdir):
+        testdir.makepyfile("""
+            class TestCase(object):
+                @property
+                def prop(self):
+                    raise NotImplementedError()
+        """)
+        result = testdir.runpytest()
+        assert result.ret == EXIT_NOTESTSCOLLECTED
+
 
 class TestGenerator:
     def test_generative_functions(self, testdir):