Update test trace writer so injected baggage metadata can be asserted as tags

Author: mcculls

dd-java-agent/testing/src/main/groovy/datadog/trace/agent/test/base/HttpServerTest.groovy

@@ -819,8 +819,7 @@ abstract class HttpServerTest<SERVER> extends WithHttpServer<SERVER> {
     if (isDataStreamsEnabled()) {
       StatsGroup first = TEST_DATA_STREAMS_WRITER.groups.find { it.parentHash == 0 }
       verifyAll(first) {
-        edgeTags.containsAll(DSM_EDGE_TAGS)
-        edgeTags.size() == DSM_EDGE_TAGS.size()
+        tags == DSM_EDGE_TAGS
       }
     }
   }

dd-trace-core/src/main/java/datadog/trace/common/writer/ListWriter.java

@@ -38,7 +38,14 @@ public void write(List<DDSpan> trace) {
     for (DDSpan span : trace) {
       // This is needed to properly do all delayed processing to make this writer even
       // remotely realistic so the test actually test something
-      span.processTagsAndBaggage(MetadataConsumer.NO_OP);
+      span.processTagsAndBaggage(metadata -> {
+        // surface injected baggage metadata as span tags so they can be asserted
+        metadata.getBaggage().forEach((k, v) -> {
+          if (!k.startsWith("_dd.") && span.getTag(k) == null) {
+            span.setTag(k, v);
+          }
+        });
+      });
     }
 
     add(trace);