unittest.UnitTestCase: Allow __test__ for methods

__test__ needs to be checked for methods of a class too. Earlier,
this was not done, and all methods in a class was assumed to be
a test. This commit adds the appropriate condition to ensure that
if the __test__ is set to False, it does not collect that method.

Fixes https://github.com/pytest-dev/pytest/issues/1558

_pytest/unittest.py

@@ -50,6 +50,8 @@ class UnitTestCase(pytest.Class):
         foundsomething = False
         for name in loader.getTestCaseNames(self.obj):
             x = getattr(self.obj, name)
+            if not getattr(x, '__test__', True):
+                continue
             funcobj = getattr(x, 'im_func', x)
             transfer_markers(funcobj, cls, module)
             yield TestCaseFunction(name, parent=self)