test extract style priority

Author: dgoffredo

test/tracer.cpp

@@ -417,26 +417,38 @@ TEST_CASE("span extraction") {
          0xabc,
          0xdef,
          nullopt},
-        {"Datadog and B3 style together",
+        {"Datadog overriding B3",
          {PropagationStyle::DATADOG, PropagationStyle::B3},
          {{"x-datadog-trace-id", "255"},
           {"x-datadog-parent-id", "14"},
           {"x-datadog-sampling-priority", "0"},
-          {"x-b3-traceid", "ff"},
-          {"x-b3-spanid", "e"},
+          {"x-b3-traceid", "fff"},
+          {"x-b3-spanid", "ef"},
           {"x-b3-sampled", "0"}},
          255,
          14,
          0},
-        {"Datadog and B3 style together without sampling priority",
+        {"Datadog overriding B3, without sampling priority",
          {PropagationStyle::DATADOG, PropagationStyle::B3},
          {{"x-datadog-trace-id", "255"},
           {"x-datadog-parent-id", "14"},
-          {"x-b3-traceid", "ff"},
-          {"x-b3-spanid", "e"}},
+          {"x-b3-traceid", "fff"},
+          {"x-b3-spanid", "ef"}},
          255,
          14,
          nullopt},
+        {"B3 after Datadog found no context",
+         {PropagationStyle::DATADOG, PropagationStyle::B3},
+         {{"x-b3-traceid", "ff"}, {"x-b3-spanid", "e"}},
+         0xff,
+         0xe,
+         nullopt},
+        {"Datadog after B3 found no context",
+         {PropagationStyle::B3, PropagationStyle::DATADOG},
+         {{"x-b3-traceid", "fff"}, {"x-b3-spanid", "ef"}},
+         0xfff,
+         0xef,
+         nullopt},
     }));
 
     CAPTURE(test_case.name);