update system tests to match spec

tests/parametric/test_headers_tracecontext.py

@@ -842,7 +842,7 @@ def test_tracestate_w3c_p_extract_datadog_first(self, test_agent, test_library):
                 http_headers=[
                     ["traceparent", "00-1111111111111111000000000000000-000000003ade68b1-01"],
                     ["tracestate", "dd=s:2;p:0123456789abcdef,foo=1"],
-                    ["x-datadog-parent-id", "9876543210"],
+                    ["x-datadog-parent-id", "123456789"],
                     ["x-datadog-trace-id", "2"],
                     ["x-datadog-tags", "_dd.p.tid=2222222222222222"],
                 ],
@@ -868,7 +868,7 @@ def test_tracestate_w3c_p_extract_datadog_first(self, test_agent, test_library):
                 http_headers=[
                     ["traceparent", "00-00000000000000000000000000000006-000000003ade68b1-01"],
                     ["tracestate", "dd=s:2,foo=1"],
-                    ["x-datadog-parent-id", "987654321"],
+                    ["x-datadog-parent-id", "123456789"],
                     ["x-datadog-tags", "_dd.p.tid=6"],
                 ],
             ):
@@ -885,26 +885,29 @@ def test_tracestate_w3c_p_extract_datadog_first(self, test_agent, test_library):
         )
 
         # 1) Datadog and tracecontext headers, trace-id and span-id match
-        # There is no need to propagate
+        # There is no need to propagate _dd.parent_id
         assert case1["name"] == "identical_trace_info"
+        assert case1["parent_id"] == "987654321"
         assert "_dd.parent_id" not in case1["meta"]
 
         # 2) trace-ids do not match
         # Datadog and tracecontext headers contain spans from different traces
-        # We can not reparent the trace
+        # We can not reparent the trace, datadog headers are used
         assert case2["name"] == "trace_ids_do_not_match"
+        assert case2["parent_id"] == "123456789"
         assert "_dd.parent_id" not in case2["meta"]
 
         # 3) Datadog and tracecontext headers, trace-id matches but parent ids do not
-        # Ensure the `p` value is used from the tracestate header
+        # Ensure the last parent id tag is set using the datadog header
         assert case3["name"] == "same_trace_non_matching_parent_ids"
-        assert case3["meta"]["_dd.parent_id"] == "000000000000000a"
+        assert case3["parent_id"] == "16"
+        assert case3["meta"]["_dd.parent_id"] == "000000003ade68b1"
 
         # 4) Datadog and tracecontext headers, parent ids do not match and p value is not present in tracestate
-        # The upstream Datadog tracer did not set `p` in tracestate, so we do not have the information
-        # to reparent the span. We should set the last datadog parent id to unknown (0000000000000000)
+        # Ensure the last parent id tag is set using the datadog header
         assert case4["name"] == "non_matching_span_missing_p_value"
-        assert case4["meta"]["_dd.parent_id"] == "0000000000000000"
+        assert case4["parent_id"] == "987654321"
+        assert case4["meta"]["_dd.parent_id"] == "00000000075bcd15"
 
 
     # W3C Phase 3 to try adding the tag if the span id matches regardless of headers order(if tracecontext is accounted)