check afe metrics when DP is enabled

Author: surbhigarg92

google-cloud-spanner/src/test/java/com/google/cloud/spanner/OpenTelemetryBuiltInMetricsTracerTest.java

@@ -269,6 +269,11 @@ public void testMetricsSingleUseQueryWithAfeEnabled() throws Exception {
       assertNotNull(attemptCountMetricData);
       assertThat(getAggregatedValue(attemptCountMetricData, expectedAttributes)).isEqualTo(1);
 
+      MetricData gfeLatencyMetricData =
+          getMetricData(metricReader, BuiltInMetricsConstant.GFE_LATENCIES_NAME);
+      double gfeLatencyValue = getAggregatedValue(gfeLatencyMetricData, expectedAttributes);
+      assertEquals(fakeServerTiming.get(), gfeLatencyValue, 0);
+
       assertFalse(
           checkIfMetricExists(metricReader, BuiltInMetricsConstant.GFE_CONNECTIVITY_ERROR_NAME));
       assertFalse(