When Flask activation is missing, do not emit a log message (#253)

If a Flask request doesn't have an active span, it just means that it
was initialized via a mechanism that doesn't run `before_request`, like
`app.test_request_context` or even manually. It is okay and
instrumentation still works.

Author: jpmelos

CHANGELOG.md

@@ -35,6 +35,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#236](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/236))
 - `opentelemetry-instrumentation-asgi`, `opentelemetry-instrumentation-falcon`, `opentelemetry-instrumentation-flask`, `opentelemetry-instrumentation-pyramid`, `opentelemetry-instrumentation-wsgi` Renamed `host.port` attribute to `net.host.port`
   ([#242](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/242))  
+- `opentelemetry-instrumentation-flask` Do not emit a warning message for request contexts created with `app.test_request_context`
+  ([#253](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/253))
 
 ## [0.16b1](https://github.com/open-telemetry/opentelemetry-python-contrib/releases/tag/v0.16b1) - 2020-11-26
 

instrumentation/opentelemetry-instrumentation-flask/src/opentelemetry/instrumentation/flask/__init__.py

@@ -149,11 +149,9 @@ def _teardown_request(exc):
 
     activation = flask.request.environ.get(_ENVIRON_ACTIVATION_KEY)
     if not activation:
-        _logger.warning(
-            "Flask environ's OpenTelemetry activation missing"
-            "at _teardown_flask_request(%s)",
-            exc,
-        )
+        # This request didn't start a span, maybe because it was created in a
+        # way that doesn't run `before_request`, like when it is created with
+        # `app.test_request_context`.
         return
 
     if exc is None: