HDFS-9743. Fix TestLazyPersistFiles#testFallbackToDiskFull in branch-2.7. Contributed by Kihwal Lee.

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -81,6 +81,8 @@ Release 2.7.3 - UNRELEASED
     HDFS-9406. FSImage may get corrupted after deleting snapshot.
     (Contributed by Jing Zhao, Stanislav Antic, Vinayakumar B, Yongjun Zhang)
 
+    HDFS-9743. Fix TestLazyPersistFiles#testFallbackToDiskFull (kihwal)
+
     HDFS-9740. Use a reasonable limit in DFSTestUtil.waitForMetric()
     (Chang Li via vinayakumarb)
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/LazyPersistTestCase.java

@@ -47,6 +47,7 @@ import org.junit.rules.Timeout;
 import java.io.File;
 import java.io.IOException;
 import java.util.Arrays;
+import java.util.concurrent.TimeoutException;
 import java.util.EnumSet;
 import java.util.List;
 import java.util.HashSet;
@@ -401,6 +402,7 @@ public abstract class LazyPersistTestCase {
 
   protected final void verifyRamDiskJMXMetric(String metricName,
       long expectedValue) throws Exception {
+    waitForMetric(metricName, (int)expectedValue);
     assertEquals(expectedValue, Integer.parseInt(jmx.getValue(metricName)));
   }
 
@@ -428,4 +430,9 @@ public abstract class LazyPersistTestCase {
       e.printStackTrace();
     }
   }
+
+  protected void waitForMetric(final String metricName, final int expectedValue)
+      throws TimeoutException, InterruptedException {
+    DFSTestUtil.waitForMetric(jmx, metricName, expectedValue);
+  }
 }