diff --git a/t/t3500-cherry.sh b/t/t3500-cherry.sh
index 3e66827d7641d8..77715318de4927 100755
--- a/t/t3500-cherry.sh
+++ b/t/t3500-cherry.sh
@@ -92,7 +92,7 @@ test_expect_success 'cherry in partial clone does bulk prefetch' '
 
 		grep "child_start.*fetch.negotiationAlgorithm" trace.output >fetches &&
 		test_line_count = 1 fetches &&
-		test_trace2_data promisor fetch_count 4 <trace.output &&
+		test_trace2_data_singular promisor fetch_count 4 <trace.output &&
 
 		# A second invocation should not refetch any blobs, since
 		# the prefetch is expected to filter out OIDs that are
diff --git a/t/t5332-multi-pack-reuse.sh b/t/t5332-multi-pack-reuse.sh
index 881ce668e1d14e..ba0826fe41e41c 100755
--- a/t/t5332-multi-pack-reuse.sh
+++ b/t/t5332-multi-pack-reuse.sh
@@ -18,11 +18,11 @@ objdir=.git/objects
 packdir=$objdir/pack
 
 test_pack_reused () {
-	test_trace2_data pack-objects pack-reused "$1"
+	test_trace2_data_singular pack-objects pack-reused "$1"
 }
 
 test_packs_reused () {
-	test_trace2_data pack-objects packs-reused "$1"
+	test_trace2_data_singular pack-objects packs-reused "$1"
 }
 
 
diff --git a/t/t5333-pseudo-merge-bitmaps.sh b/t/t5333-pseudo-merge-bitmaps.sh
index 305d6771082d55..07d2f0d9922d68 100755
--- a/t/t5333-pseudo-merge-bitmaps.sh
+++ b/t/t5333-pseudo-merge-bitmaps.sh
@@ -15,15 +15,15 @@ test_pseudo_merge_commits () {
 }
 
 test_pseudo_merges_satisfied () {
-	test_trace2_data bitmap pseudo_merges_satisfied "$1"
+	test_trace2_data_singular bitmap pseudo_merges_satisfied "$1"
 }
 
 test_pseudo_merges_cascades () {
-	test_trace2_data bitmap pseudo_merges_cascades "$1"
+	test_trace2_data_singular bitmap pseudo_merges_cascades "$1"
 }
 
 test_pseudo_merges_reused () {
-	test_trace2_data pack-bitmap-write building_bitmaps_pseudo_merge_reused "$1"
+	test_trace2_data_singular pack-bitmap-write building_bitmaps_pseudo_merge_reused "$1"
 }
 
 tag_everything () {
diff --git a/t/t5620-backfill.sh b/t/t5620-backfill.sh
index d2ea68e065304d..4e2073c1defb1d 100755
--- a/t/t5620-backfill.sh
+++ b/t/t5620-backfill.sh
@@ -116,7 +116,7 @@ test_expect_success 'do partial clone 1, backfill gets all objects' '
 		-C backfill1 backfill &&
 
 	# We should have engaged the partial clone machinery
-	test_trace2_data promisor fetch_count 48 <backfill-file-trace &&
+	test_trace2_data_singular promisor fetch_count 48 <backfill-file-trace &&
 
 	# No more missing objects!
 	git -C backfill1 rev-list --quiet --objects --missing=print HEAD >revs2 &&
@@ -160,8 +160,8 @@ test_expect_success 'backfill --sparse' '
 	# older versions of the four files at tip.
 	GIT_TRACE2_EVENT="$(pwd)/sparse-trace1" git \
 		-C backfill3 backfill --sparse &&
-	test_trace2_data promisor fetch_count 4 <sparse-trace1 &&
-	test_trace2_data path-walk paths 5 <sparse-trace1 &&
+	test_trace2_data_singular promisor fetch_count 4 <sparse-trace1 &&
+	test_trace2_data_singular path-walk paths 5 <sparse-trace1 &&
 	git -C backfill3 rev-list --quiet --objects --missing=print HEAD >missing &&
 	test_line_count = 40 missing &&
 
@@ -172,8 +172,8 @@ test_expect_success 'backfill --sparse' '
 	git -C backfill3 sparse-checkout set d &&
 	GIT_TRACE2_EVENT="$(pwd)/sparse-trace2" git \
 		-C backfill3 backfill --sparse &&
-	test_trace2_data promisor fetch_count 8 <sparse-trace2 &&
-	test_trace2_data path-walk paths 15 <sparse-trace2 &&
+	test_trace2_data_singular promisor fetch_count 8 <sparse-trace2 &&
+	test_trace2_data_singular path-walk paths 15 <sparse-trace2 &&
 	git -C backfill3 rev-list --quiet --objects --missing=print HEAD >missing &&
 	test_line_count = 24 missing &&
 
@@ -194,8 +194,8 @@ test_expect_success 'backfill auto-detects sparse-checkout from config' '
 	GIT_TRACE2_EVENT="$(pwd)/auto-sparse-trace" git \
 		-C backfill-auto-sparse backfill &&
 
-	test_trace2_data promisor fetch_count 4 <auto-sparse-trace &&
-	test_trace2_data path-walk paths 5 <auto-sparse-trace
+	test_trace2_data_singular promisor fetch_count 4 <auto-sparse-trace &&
+	test_trace2_data_singular path-walk paths 5 <auto-sparse-trace
 '
 
 test_expect_success 'backfill --sparse without cone mode (positive)' '
@@ -218,10 +218,10 @@ test_expect_success 'backfill --sparse without cone mode (positive)' '
 
 	GIT_TRACE2_EVENT="$(pwd)/no-cone-trace1" git \
 		-C backfill4 backfill --sparse &&
-	test_trace2_data promisor fetch_count 6 <no-cone-trace1 &&
+	test_trace2_data_singular promisor fetch_count 6 <no-cone-trace1 &&
 
 	# This walk needed to visit all directories to search for these paths.
-	test_trace2_data path-walk paths 12 <no-cone-trace1 &&
+	test_trace2_data_singular path-walk paths 12 <no-cone-trace1 &&
 	git -C backfill4 rev-list --quiet --objects --missing=print HEAD >missing &&
 	test_line_count = 36 missing
 '
@@ -246,11 +246,11 @@ test_expect_success 'backfill --sparse without cone mode (negative)' '
 
 	GIT_TRACE2_EVENT="$(pwd)/no-cone-trace2" git \
 		-C backfill5 backfill --sparse &&
-	test_trace2_data promisor fetch_count 18 <no-cone-trace2 &&
+	test_trace2_data_singular promisor fetch_count 18 <no-cone-trace2 &&
 
 	# This walk needed to visit all directories to search for these paths, plus
 	# 12 extra "file.?.txt" paths than the previous test.
-	test_trace2_data path-walk paths 24 <no-cone-trace2 &&
+	test_trace2_data_singular path-walk paths 24 <no-cone-trace2 &&
 	git -C backfill5 rev-list --quiet --objects --missing=print HEAD >missing &&
 	test_line_count = 12 missing
 '
@@ -268,7 +268,7 @@ test_expect_success 'backfill with revision range' '
 	GIT_TRACE2_EVENT="$(pwd)/backfill-trace" git -C backfill-revs backfill HEAD~2..HEAD &&
 
 	# 36 objects downloaded, 12 still missing
-	test_trace2_data promisor fetch_count 36 <backfill-trace &&
+	test_trace2_data_singular promisor fetch_count 36 <backfill-trace &&
 	git -C backfill-revs rev-list --quiet --objects --missing=print HEAD >missing &&
 	test_line_count = 12 missing
 '
@@ -288,10 +288,10 @@ test_expect_success 'backfill with revisions over stdin' '
 	^HEAD~2
 	EOF
 
-	GIT_TRACE2_EVENT="$(pwd)/backfill-trace" git -C backfill-revs backfill --stdin <in &&
+	GIT_TRACE2_EVENT="$(pwd)/backfill-stdin-trace" git -C backfill-revs backfill --stdin <in &&
 
 	# 36 objects downloaded, 12 still missing
-	test_trace2_data promisor fetch_count 36 <backfill-trace &&
+	test_trace2_data_singular promisor fetch_count 36 <backfill-stdin-trace &&
 	git -C backfill-revs rev-list --quiet --objects --missing=print HEAD >missing &&
 	test_line_count = 12 missing
 '
@@ -523,7 +523,7 @@ test_expect_success 'backfilling over HTTP succeeds' '
 		-C backfill-http backfill &&
 
 	# We should have engaged the partial clone machinery
-	test_trace2_data promisor fetch_count 48 <backfill-http-trace &&
+	test_trace2_data_singular promisor fetch_count 48 <backfill-http-trace &&
 
 	# Confirm all objects are present, none missing.
 	git -C backfill-http rev-list --objects --all >rev-list-out &&
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index d61c4a4d73c390..3f8f4723956223 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -1964,8 +1964,8 @@ test_expect_success 'grep of revision in partial clone batches prefetch and hono
 
 	# Exactly the two a/*.txt blobs should have been requested, and
 	# the server packed those two objects in the response.
-	test_trace2_data promisor fetch_count 2 <grep-trace-pathspec &&
-	test_trace2_data pack-objects written 2 <grep-trace-pathspec &&
+	test_trace2_data_singular promisor fetch_count 2 <grep-trace-pathspec &&
+	test_trace2_data_singular pack-objects written 2 <grep-trace-pathspec &&
 
 	# b/matches.md should still be missing locally.
 	git -C grep-partial rev-list --quiet --objects \
@@ -1979,8 +1979,8 @@ test_expect_success 'grep of revision in partial clone batches prefetch and hono
 		git -C grep-partial grep -c "needle" HEAD >result &&
 
 	test_line_count = 2 result &&
-	test_trace2_data promisor fetch_count 1 <grep-trace-all &&
-	test_trace2_data pack-objects written 1 <grep-trace-all &&
+	test_trace2_data_singular promisor fetch_count 1 <grep-trace-all &&
+	test_trace2_data_singular pack-objects written 1 <grep-trace-all &&
 
 	# Everything is local now.
 	git -C grep-partial rev-list --quiet --objects \
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 809c6621241944..026cf0ef332dbe 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1996,6 +1996,41 @@ test_trace2_data () {
 	grep -e '"category":"'"$1"'","key":"'"$2"'","value":"'"$3"'"'
 }
 
+# Check that the given trace2 data event has the expected value and
+# appears exactly once.  Produces a diagnostic on failure.
+#
+#	test_trace2_data_singular <category> <key> <value>
+test_trace2_data_singular () {
+	local category="$1" key="$2" expect_val="$3"
+	local kv_pattern='"category":"'"$category"'","key":"'"$key"'","value":"\([^"]*\)"'
+	local actual
+
+	actual=$(sed -n "s|.*${kv_pattern}.*|\1|p") &&
+
+	if test -z "$actual"
+	then
+		echo >&4 "error: trace2 data '$category/$key' not found"
+		return 1
+	fi &&
+
+	case "$actual" in
+	*"
+"*)
+		echo >&4 "error: trace2 data '$category/$key' has multiple entries, expected 1"
+		printf '%s\n' "$actual" | sed 's/^/  actual:   /' >&4
+		return 1
+		;;
+	esac &&
+
+	if test "$actual" != "$expect_val"
+	then
+		echo >&4 "error: trace2 data '$category/$key'"
+		echo >&4 "  expected: $expect_val"
+		echo >&4 "  actual:   $actual"
+		return 1
+	fi
+}
+
 # Given a GIT_TRACE2_EVENT log over stdin, writes to stdout a list of URLs
 # sent to git-remote-https child processes.
 test_remote_https_urls() {