Migrate the skip_unless_attr decorator from tempest

This commit migrates the skip_unless_attr from tempest to
tempest-lib.

Change-Id: I6a1e7a411a4b27fa0f9bd533276d5cb4d4759976

tempest_lib/decorators.py

@@ -59,3 +59,22 @@ def idempotent_id(id):
             f.__doc__ = 'Test idempotent id: %s' % id
         return f
     return decorator
+
+
+class skip_unless_attr(object):
+    """Decorator to skip tests if a specified attr does not exists or False"""
+    def __init__(self, attr, msg=None):
+        self.attr = attr
+        self.message = msg or ("Test case attribute %s not found "
+                               "or False") % attr
+
+    def __call__(self, func):
+        def _skipper(*args, **kw):
+            """Wrapped skipper function."""
+            testobj = args[0]
+            if not getattr(testobj, self.attr, False):
+                raise testtools.TestCase.skipException(self.message)
+            func(*args, **kw)
+        _skipper.__name__ = func.__name__
+        _skipper.__doc__ = func.__doc__
+        return _skipper

tempest_lib/tests/test_decorators.py

@@ -95,3 +95,32 @@ class TestIdempotentIdDecorator(base.TestCase):
     def test_idempotent_id_not_valid_uuid(self):
         _id = '42'
         self.assertRaises(ValueError, self._test_helper, _id)
+
+
+class TestSkipUnlessAttrDecorator(base.TestCase):
+    def _test_skip_unless_attr(self, attr, expected_to_skip=True):
+        class TestFoo(test.BaseTestCase):
+            expected_attr = not expected_to_skip
+
+            @decorators.skip_unless_attr(attr)
+            def test_foo(self):
+                pass
+
+        t = TestFoo('test_foo')
+        if expected_to_skip:
+            self.assertRaises(testtools.TestCase.skipException,
+                              t.test_foo())
+        else:
+            try:
+                t.test_foo()
+            except Exception:
+                raise testtools.TestCase.failureException()
+
+    def test_skip_attr_does_not_exist(self):
+        self._test_skip_unless_attr('unexpected_attr')
+
+    def test_skip_attr_false(self):
+        self._test_skip_unless_attr('expected_attr')
+
+    def test_no_skip_for_attr_exist_and_true(self):
+        self._test_skip_unless_attr('expected_attr', expected_to_skip=False)