diff --git a/flow/Tracing.actor.cpp b/flow/Tracing.actor.cpp
index a709cfadfe1..b84f1da381b 100644
--- a/flow/Tracing.actor.cpp
+++ b/flow/Tracing.actor.cpp
@@ -22,7 +22,6 @@
 #include "flow/IRandom.h"
 #include "flow/UnitTest.h"
 #include "flow/Knobs.h"
-#include "fdbclient/IKnobCollection.h"
 #include "flow/network.h"
 #include <functional>
 #include <iomanip>
@@ -529,36 +528,6 @@ TEST_CASE("/flow/Tracing/AddEvents") {
 	return Void();
 };
 
-TEST_CASE("/flow/Tracing/AddAttributes") {
-	Span span1("span_with_attrs"_loc,
-	           SpanContext(deterministicRandom()->randomUniqueID(),
-	                       deterministicRandom()->randomUInt64(),
-	                       TraceFlags::sampled));
-	IKnobCollection::getMutableGlobalKnobCollection().setKnob("tracing_span_attributes_enabled",
-	                                                          KnobValueRef::create(bool{ true }));
-	auto arena = span1.arena;
-	span1.addAttribute(StringRef(arena, LiteralStringRef("foo")), StringRef(arena, LiteralStringRef("bar")));
-	span1.addAttribute(StringRef(arena, LiteralStringRef("operation")), StringRef(arena, LiteralStringRef("grv")));
-	ASSERT_EQ(span1.attributes.size(), 3); // Includes default attribute of "address"
-	ASSERT(span1.attributes[1] == KeyValueRef("foo"_sr, "bar"_sr));
-	ASSERT(span1.attributes[2] == KeyValueRef("operation"_sr, "grv"_sr));
-
-	Span span2("span_with_attrs"_loc,
-	           SpanContext(deterministicRandom()->randomUniqueID(),
-	                       deterministicRandom()->randomUInt64(),
-	                       TraceFlags::sampled));
-	auto s2Arena = span2.arena;
-	span2.addAttribute(StringRef(s2Arena, LiteralStringRef("a")), StringRef(s2Arena, LiteralStringRef("1")))
-	    .addAttribute(StringRef(s2Arena, LiteralStringRef("b")), LiteralStringRef("2"))
-	    .addAttribute(StringRef(s2Arena, LiteralStringRef("c")), LiteralStringRef("3"));
-
-	ASSERT_EQ(span2.attributes.size(), 4); // Includes default attribute of "address"
-	ASSERT(span2.attributes[1] == KeyValueRef("a"_sr, "1"_sr));
-	ASSERT(span2.attributes[2] == KeyValueRef("b"_sr, "2"_sr));
-	ASSERT(span2.attributes[3] == KeyValueRef("c"_sr, "3"_sr));
-	return Void();
-};
-
 TEST_CASE("/flow/Tracing/AddLinks") {
 	Span span1("span_with_links"_loc);
 	ASSERT(!span1.context.isSampled());
@@ -651,11 +620,42 @@ std::string readMPString(uint8_t* index) {
 	return reinterpret_cast<char*>(data);
 }
 
+class AccessAttrsUnitTest {
+public:
+	void RunAddAttributes();
+	void RunFastUDPMessagePackEncoding();
+};
+void AccessAttrsUnitTest::RunAddAttributes() {
+	Span span1("span_with_attrs"_loc,
+	           SpanContext(deterministicRandom()->randomUniqueID(),
+	                       deterministicRandom()->randomUInt64(),
+	                       TraceFlags::sampled));
+	auto arena = span1.arena;
+	span1.addAttribute(StringRef(arena, LiteralStringRef("foo")), StringRef(arena, LiteralStringRef("bar")), true);
+	span1.addAttribute(
+	    StringRef(arena, LiteralStringRef("operation")), StringRef(arena, LiteralStringRef("grv")), true);
+	ASSERT_EQ(span1.attributes.size(), 3); // Includes default attribute of "address"
+	ASSERT(span1.attributes[1] == KeyValueRef("foo"_sr, "bar"_sr));
+	ASSERT(span1.attributes[2] == KeyValueRef("operation"_sr, "grv"_sr));
+
+	Span span2("span_with_attrs"_loc,
+	           SpanContext(deterministicRandom()->randomUniqueID(),
+	                       deterministicRandom()->randomUInt64(),
+	                       TraceFlags::sampled));
+	auto s2Arena = span2.arena;
+	span2.addAttribute(StringRef(s2Arena, LiteralStringRef("a")), StringRef(s2Arena, LiteralStringRef("1")), true)
+	    .addAttribute(StringRef(s2Arena, LiteralStringRef("b")), LiteralStringRef("2"), true)
+	    .addAttribute(StringRef(s2Arena, LiteralStringRef("c")), LiteralStringRef("3"), true);
+
+	ASSERT_EQ(span2.attributes.size(), 4); // Includes default attribute of "address"
+	ASSERT(span2.attributes[1] == KeyValueRef("a"_sr, "1"_sr));
+	ASSERT(span2.attributes[2] == KeyValueRef("b"_sr, "2"_sr));
+	ASSERT(span2.attributes[3] == KeyValueRef("c"_sr, "3"_sr));
+}
+
+void AccessAttrsUnitTest::RunFastUDPMessagePackEncoding() {
 // Windows doesn't like lack of header and declaration of constructor for FastUDPTracer
 #ifndef WIN32
-TEST_CASE("/flow/Tracing/FastUDPMessagePackEncoding") {
-	IKnobCollection::getMutableGlobalKnobCollection().setKnob("tracing_span_attributes_enabled",
-	                                                          KnobValueRef::create(bool{ true }));
 	Span span1("encoded_span"_loc);
 	auto request = TraceRequest{ .buffer = std::make_unique<uint8_t[]>(kTraceBufferSize),
 		                         .data_size = 0,
@@ -716,7 +716,7 @@ TEST_CASE("/flow/Tracing/FastUDPMessagePackEncoding") {
 	auto s3Arena = span3.arena;
 	SmallVectorRef<KeyValueRef> attrs;
 	attrs.push_back(s3Arena, KeyValueRef("foo"_sr, "bar"_sr));
-	span3.addAttribute("operation"_sr, "grv"_sr)
+	span3.addAttribute("operation"_sr, "grv"_sr, true)
 	    .addLink(SpanContext(UID(300, 301), 400, TraceFlags::sampled))
 	    .addEvent(StringRef(s3Arena, LiteralStringRef("event1")), 100.101, attrs);
 	tracer.serialize_span(span3, request);
@@ -792,6 +792,17 @@ TEST_CASE("/flow/Tracing/FastUDPMessagePackEncoding") {
 	// Read and verify span name
 	ASSERT(data[37] == 0xda);
 	ASSERT(readMPString(&data[37]) == longString);
+#endif
+};
+
+TEST_CASE("/flow/Tracing/AddAttributes") {
+	AccessAttrsUnitTest test;
+	test.RunAddAttributes();
+	return Void();
+};
+
+TEST_CASE("/flow/Tracing/FastUDPMessagePackEncoding") {
+	AccessAttrsUnitTest test;
+	test.RunFastUDPMessagePackEncoding();
 	return Void();
 };
-#endif
diff --git a/flow/Tracing.h b/flow/Tracing.h
index 30c2161b1a1..c33cdc52451 100644
--- a/flow/Tracing.h
+++ b/flow/Tracing.h
@@ -114,6 +114,8 @@ struct SpanEventRef {
 };
 
 class Span {
+	friend class AccessAttrsUnitTest;
+
 public:
 	// Construct a Span with a given context, location, parentContext and optional links.
 	//
@@ -226,10 +228,7 @@ class Span {
 	}
 
 	Span& addAttribute(const StringRef& key, const StringRef& value) {
-		if (FLOW_KNOBS->TRACING_SPAN_ATTRIBUTES_ENABLED) {
-			attributes.push_back_deep(arena, KeyValueRef(key, value));
-		}
-		return *this;
+		return addAttribute(key, value, FLOW_KNOBS->TRACING_SPAN_ATTRIBUTES_ENABLED);
 	}
 
 	Span& setParent(const SpanContext& parent) {
@@ -250,6 +249,15 @@ class Span {
 	SmallVectorRef<KeyValueRef> attributes; // not necessarily sorted
 	SmallVectorRef<SpanEventRef> events;
 	SpanStatus status;
+
+private:
+	// For unit testing only.
+	Span& addAttribute(const StringRef& key, const StringRef& value, bool tracingAttrsEnabled) {
+		if (tracingAttrsEnabled) {
+			attributes.push_back_deep(arena, KeyValueRef(key, value));
+		}
+		return *this;
+	}
 };
 
 // The user selects a tracer using a string passed to fdbserver on boot.