chore(fix): unflake MetricsTracerTest (#313)

* chore(fix): unflake MetricsTracerTest

* chore(fix): unflake MetricsTracerTest

* chore(fix): unflake MetricsTracerTest

* chore(fix): unflake MetricsTracerTest

* review feedback

* review feedback

Author: kolea2

google-cloud-bigtable/src/test/java/com/google/cloud/bigtable/data/v2/stub/metrics/MetricsTracerTest.java

@@ -237,7 +237,10 @@ public Object answer(InvocationOnMock invocation) throws Throwable {
         getAggregationValueAsLong(
             RpcViewConstants.BIGTABLE_READ_ROWS_FIRST_ROW_LATENCY_VIEW,
             ImmutableMap.<TagKey, TagValue>of());
-    assertThat(firstRowLatency).isIn(Range.closed(beforeSleep, elapsed - afterSleep));
+
+    // adding buffer time to the upper range to allow for a race between the emulator and the client
+    // recording the duration
+    assertThat(firstRowLatency).isIn(Range.closed(beforeSleep, elapsed - afterSleep / 2));
   }
 
   @Test