SOLR-16960 Tests should sometimes run with a Tracer (not no-op) (#1972)

solr/core/src/java/org/apache/solr/servlet/ServletUtils.java

@@ -236,7 +236,7 @@ private static void traceHttpRequestExecution2(
     try (var scope = context.with(span).makeCurrent()) {
       assert scope != null; // prevent javac warning about scope being unused
       TraceUtils.setSpan(request, span);
-      TraceUtils.ifNotNoop(
+      TraceUtils.ifValidTraceId(
           span, s -> MDCLoggingContext.setTracerId(s.getSpanContext().getTraceId()));
       tracedExecution.run();
     } catch (ExceptionWhileTracing e) {

solr/core/src/java/org/apache/solr/util/tracing/TraceUtils.java

@@ -21,6 +21,7 @@
 import io.opentelemetry.api.trace.Span;
 import io.opentelemetry.api.trace.SpanBuilder;
 import io.opentelemetry.api.trace.SpanKind;
+import io.opentelemetry.api.trace.TraceId;
 import io.opentelemetry.api.trace.Tracer;
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.propagation.TextMapPropagator;
@@ -108,6 +109,20 @@ public static void ifNotNoop(Span span, Consumer<Span> consumer) {
     }
   }
 
+  /**
+   * Sometimes the tests will use a recoding noop span to verify the complete code path so we need
+   * to distinguish this case and only perform a specific operation (like updating the MDC context)
+   * only in case the generated trace id is valid
+   *
+   * @param span current span
+   * @param consumer consumer to be called
+   */
+  public static void ifValidTraceId(Span span, Consumer<Span> consumer) {
+    if (TraceId.isValid(span.getSpanContext().getTraceId())) {
+      consumer.accept(span);
+    }
+  }
+
   public static void setSpan(HttpServletRequest req, Span span) {
     req.setAttribute(REQ_ATTR_TRACING_SPAN, span);
   }