Update potential misunderstanding about thread safety

tests/test_metric.cpp

@@ -402,21 +402,22 @@ TEST_CASE("thread safety") {
     }
   }
 
-  SUBCASE("gauge multi-writer with CAS") {
+  SUBCASE("gauge multi-writer contention") {
     auto gauge_family =
         metric::create_gauge("thread_test_gauge", "Thread test gauge");
-    auto shared_gauge = gauge_family.create({{"shared", "true"}});
 
     std::vector<std::thread> threads;
     std::latch start_latch{num_threads};
 
-    // Multiple threads writing to same gauge (uses atomic CAS)
+    // Multiple threads create gauges with the same labels, writing to the same
+    // underlying state, testing CAS contention.
     for (int i = 0; i < num_threads; ++i) {
       threads.emplace_back([&]() {
+        auto gauge = gauge_family.create({{"shared", "true"}});
         start_latch.arrive_and_wait();
 
         for (int j = 0; j < ops_per_thread; ++j) {
-          shared_gauge.inc(1.0);
+          gauge.inc(1.0);
         }
       });
     }