api: Add reset for configuration testing (#636)

It is a common occurrence in tests that the global Configuration object needs to be "reset" between tests. This means that its attributes need to be set back to their original values. Since the Configuration object is immutable by design, some additional, non-production available mechanism is needed to perform this action.

The need for this feature was mentioned in a conversation in #630.

ext/opentelemetry-ext-flask/tests/base_test.py

@@ -19,6 +19,7 @@
 from werkzeug.wrappers import BaseResponse
 
 from opentelemetry import trace
+from opentelemetry.configuration import Configuration
 
 
 def expected_attributes(override_attributes):
@@ -40,6 +41,10 @@ def expected_attributes(override_attributes):
 
 
 class InstrumentationTest:
+    def setUp(self):  # pylint: disable=invalid-name
+        super().setUp()  # pylint: disable=no-member
+        Configuration._reset()  # pylint: disable=protected-access
+
     @staticmethod
     def _hello_endpoint(helloid):
         if helloid == 500:

ext/opentelemetry-ext-flask/tests/test_automatic.py

@@ -16,7 +16,6 @@
 from werkzeug.test import Client
 from werkzeug.wrappers import BaseResponse
 
-from opentelemetry.configuration import Configuration
 from opentelemetry.ext.flask import FlaskInstrumentor
 from opentelemetry.test.test_base import TestBase
 from opentelemetry.test.wsgitestutil import WsgiTestBase
@@ -29,8 +28,6 @@ class TestAutomatic(InstrumentationTest, TestBase, WsgiTestBase):
     def setUp(self):
         super().setUp()
 
-        Configuration._instance = None  # pylint: disable=protected-access
-        Configuration.__slots__ = []  # pylint: disable=protected-access
         FlaskInstrumentor().instrument()
 
         self.app = flask.Flask(__name__)

ext/opentelemetry-ext-flask/tests/test_programmatic.py

@@ -14,7 +14,6 @@
 
 from flask import Flask
 
-from opentelemetry.configuration import Configuration
 from opentelemetry.ext.flask import FlaskInstrumentor
 from opentelemetry.test.test_base import TestBase
 from opentelemetry.test.wsgitestutil import WsgiTestBase
@@ -27,8 +26,6 @@ class TestProgrammatic(InstrumentationTest, TestBase, WsgiTestBase):
     def setUp(self):
         super().setUp()
 
-        Configuration._instance = None  # pylint: disable=protected-access
-        Configuration.__slots__ = []  # pylint: disable=protected-access
         self.app = Flask(__name__)
 
         FlaskInstrumentor().instrument_app(self.app)

opentelemetry-api/src/opentelemetry/configuration/__init__.py

@@ -122,3 +122,20 @@ def __new__(cls) -> "Configuration":
 
     def __getattr__(self, name):
         return None
+
+    @classmethod
+    def _reset(cls):
+        """
+        This method "resets" the global configuration attributes
+
+        It is not intended to be used by production code but by testing code
+        only.
+        """
+
+        for slot in cls.__slots__:
+            if slot in cls.__dict__.keys():
+                delattr(cls, slot)
+                delattr(cls, "_{}".format(slot))
+
+        cls.__slots__ = []
+        cls._instance = None

opentelemetry-api/tests/configuration/test_configuration.py

@@ -20,14 +20,10 @@
 
 
 class TestConfiguration(TestCase):
-    def setUp(self):
-        # This is added here to force a reload of the whole Configuration
-        # class, resetting its internal attributes so that each tests starts
-        # with a clean class.
-        from opentelemetry.configuration import Configuration  # type: ignore
-
     def tearDown(self):
-        from opentelemetry.configuration import Configuration  # type: ignore
+        # This call resets the attributes of the Configuration class so that
+        # each test is executed in the same conditions.
+        Configuration._reset()
 
     def test_singleton(self):
         self.assertIsInstance(Configuration(), Configuration)
@@ -72,3 +68,23 @@ def test_slots(self):
 
     def test_getattr(self):
         self.assertIsNone(Configuration().XYZ)
+
+    def test_reset(self):
+        environ_patcher = patch.dict(
+            "os.environ",  # type: ignore
+            {"OPENTELEMETRY_PYTHON_TRACER_PROVIDER": "tracer_provider"},
+        )
+
+        environ_patcher.start()
+
+        self.assertEqual(
+            Configuration().TRACER_PROVIDER, "tracer_provider"
+        )  # pylint: disable=no-member
+
+        environ_patcher.stop()
+
+        Configuration._reset()
+
+        self.assertIsNone(
+            Configuration().TRACER_PROVIDER
+        )  # pylint: disable=no-member