Add missing `__test__` check for test discovery.

CHANGELOG.rst

@@ -13,6 +13,10 @@ New Features
 Changes
 -------
 
+* It is now possible to skip test classes from being collected by setting a
+  ``__test__`` attribute to ``False`` in the class body (`#2007`_). Thanks
+  to `@syre`_ for the report and `@lwm`_ for the PR.
+
 * Testcase reports with a ``url`` attribute will now properly write this to junitxml.
   Thanks `@fushi`_ for the PR (`#1874`_).
 
@@ -71,6 +75,7 @@ Changes
 
 *
 
+.. _@syre: https://github.com/syre
 .. _@dupuy: https://bitbucket.org/dupuy/
 .. _@lwm: https://github.com/lwm
 .. _@adler-j: https://github.com/adler-j
@@ -83,6 +88,7 @@ Changes
 .. _#2038: https://github.com/pytest-dev/pytest/issues/2038
 .. _#2078: https://github.com/pytest-dev/pytest/issues/2078
 .. _#2082: https://github.com/pytest-dev/pytest/issues/2082
+.. _#2007: https://github.com/pytest-dev/pytest/issues/2007
 
 
 3.0.4

_pytest/compat.py

@@ -200,7 +200,7 @@ def safe_getattr(object, name, default):
     """ Like getattr but return default upon any Exception.
 
     Attribute access can potentially fail for 'evil' Python objects.
-    See issue214
+    See issue #214.
     """
     try:
         return getattr(object, name, default)

_pytest/python.py

@@ -503,6 +503,8 @@ def _get_xunit_func(obj, name):
 class Class(PyCollector):
     """ Collector for test methods. """
     def collect(self):
+        if not safe_getattr(self.obj, "__test__", True):
+            return []
         if hasinit(self.obj):
             self.warn("C1", "cannot collect test class %r because it has a "
                 "__init__ constructor" % self.obj.__name__)

testing/test_collection.py

@@ -85,6 +85,22 @@ class TestCollector:
         assert len(nodes) == 1
         assert isinstance(nodes[0], pytest.File)
 
+    def test_can_skip_class_with_test_attr(self, testdir):
+        """Assure test class is skipped when using `__test__=False` (See #2007)."""
+        testdir.makepyfile("""
+            class TestFoo():
+                __test__ = False
+                def __init__(self):
+                    pass
+                def test_foo():
+                    assert True
+        """)
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines([
+            'collected 0 items',
+            '*no tests ran in*',
+        ])
+
 class TestCollectFS:
     def test_ignored_certain_directories(self, testdir):
         tmpdir = testdir.tmpdir