fix flaky test

drain metric collector singleton before each test

Author: jpbempel

dd-trace-core/src/test/java/datadog/trace/core/baggage/BaggagePropagatorTelemetryTest.java

@@ -16,13 +16,21 @@
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 class BaggagePropagatorTelemetryTest {
 
   private static final CarrierVisitor<Map<String, String>> MAP_VISITOR =
       (map, consumer) -> map.forEach(consumer);
 
+  @BeforeEach
+  void setup() {
+    // Drain any metrics accumulated by other tests
+    CoreMetricCollector.getInstance().prepareMetrics();
+    CoreMetricCollector.getInstance().drain();
+  }
+
   @Test
   void shouldDirectlyIncrementBaggageMetrics() {
     BaggageMetrics baggageMetrics = BaggageMetrics.getInstance();