diff --git a/internal/observability/bytes_test.go b/internal/observability/bytes_test.go
new file mode 100644
index 00000000..5f7d8316
--- /dev/null
+++ b/internal/observability/bytes_test.go
@@ -0,0 +1,29 @@
+package observability
+
+import (
+	"testing"
+)
+
+func TestFormatBytesBelow1KB(t *testing.T) {
+	if got := formatBytes(512.0); got != "512B" {
+		t.Fatalf("got %q, want %q", got, "512B")
+	}
+}
+
+func TestFormatBytesInKB(t *testing.T) {
+	if got := formatBytes(2048.0); got != "2.0KB" {
+		t.Fatalf("got %q, want %q", got, "2.0KB")
+	}
+}
+
+func TestFormatBytesInMB(t *testing.T) {
+	if got := formatBytes(5_242_880.0); got != "5.0MB" {
+		t.Fatalf("got %q, want %q", got, "5.0MB")
+	}
+}
+
+func TestFormatBytesReturnsStringAsIs(t *testing.T) {
+	if got := formatBytes("unknown"); got != "unknown" {
+		t.Fatalf("got %q, want %q", got, "unknown")
+	}
+}