Addressing review feedback

Fixing incorrect type annotation for WSGI getter for
HTTPTextFormatter.

Using setdefautl to enable more atomic and simple
setting of headers.

Using UnitTest style assertions vs PyTest.

ext/opentelemetry-ext-http-requests/src/opentelemetry/ext/http_requests/__init__.py

@@ -74,11 +74,10 @@ def instrumented_request(self, method, url, *args, **kwargs):
             # TODO: Propagate the trace context via headers once we have a way
             # to access propagators.
 
-            headers = kwargs.get("headers", {})
+            headers = kwargs.setdefault("headers", {})
             propagator.get_global_propagator().inject(
                 tracer, type(headers).__setitem__, headers
             )
-            kwargs["headers"] = headers
             result = wrapped(self, method, url, *args, **kwargs)  # *** PROCEED
 
             span.set_attribute("http.status_code", result.status_code)

ext/opentelemetry-ext-wsgi/src/opentelemetry/ext/wsgi/__init__.py

@@ -104,11 +104,14 @@ def __call__(self, environ, start_response):
 
 def get_header_from_environ(
     environ: dict, header_name: str
-) -> typing.Optional[str]:
+) -> typing.List[str]:
     """Retrieve the header value from the wsgi environ dictionary.
 
     Returns:
         A string with the header value if it exists, else None.
     """
     environ_key = "HTTP_" + header_name.upper().replace("-", "_")
-    return [environ.get(environ_key)]
+    value = environ.get(environ_key)
+    if value:
+        return [value]
+    return []

opentelemetry-example-app/tests/test_flask_example.py

@@ -53,5 +53,7 @@ def test_full_path(self):
         prepared_request = self.send.call_args[0][1]
         headers = prepared_request.headers
         for required_header in {"x-b3-traceid", "x-b3-spanid", "x-b3-sampled"}:
-            assert required_header in headers
-        assert headers["x-b3-traceid"] == b3_format.format_trace_id(trace_id)
+            self.assertIn(required_header, headers)
+        self.assertEqual(
+            headers["x-b3-traceid"], b3_format.format_trace_id(trace_id)
+        )