Add fixture_property decorator

Add a new decorator that improve property decorator
by allowing to invoke getter method from fixture class.

This makes below code to work:

import tobiko

class MyFixture(tobiko.SharedFixture):

  @tobiko.fixture_property
  def my_property():
      return ...

assert tibiko.get_fixture(MyFixture).my_property == MyFixture.my_property

Change-Id: I72b6b8305823bb7be2bee6a806a6bced915229f6

tobiko/__init__.py

@@ -28,6 +28,7 @@ TobikoException = _exception.TobikoException
 
 is_fixture = _fixture.is_fixture
 get_fixture = _fixture.get_fixture
+fixture_property = _fixture.fixture_property
 required_fixture = _fixture.required_fixture
 required_setup_fixture = _fixture.required_setup_fixture
 get_fixture_name = _fixture.get_fixture_name

tobiko/common/_fixture.py

@@ -215,6 +215,10 @@ def init_fixture(obj, name):
     raise TypeError("Invalid fixture object type: {!r}".format(obj))
 
 
+def fixture_property(*args, **kwargs):
+    return FixtureProperty(*args, **kwargs)
+
+
 def required_fixture(obj):
     '''Creates a property that gets fixture identified by given :param obj:
 
@@ -371,6 +375,13 @@ class SharedFixture(fixtures.Fixture):
         pass
 
 
+class FixtureProperty(property):
+
+    def __get__(self, instance, owner):
+        instance = instance or tobiko.get_fixture(owner)
+        return super(FixtureProperty, self).__get__(instance, owner)
+
+
 class RequiredFixtureProperty(object):
 
     def __init__(self, fixture):

tobiko/tests/test_fixture.py

@@ -208,6 +208,24 @@ class CleanupFixtureTest(FixtureBaseTest):
         result.cleanup_fixture.assert_called_once_with()
 
 
+class MyFixtureWithProperty(MyBaseFixture):
+
+    @tobiko.fixture_property
+    def some_property(self):
+        return id(self)
+
+
+class FixturePropertyTest(FixtureBaseTest):
+
+    def test_with_instance(self):
+        fixture = tobiko.get_fixture(MyFixtureWithProperty)
+        self.assertEqual(id(fixture), fixture.some_property)
+
+    def test_without_instance(self):
+        fixture = tobiko.get_fixture(MyFixtureWithProperty)
+        self.assertEqual(id(fixture), MyFixtureWithProperty.some_property)
+
+
 class MyFixture2(MyBaseFixture):
     pass