improves TabletServerGivesUpIT (apache#4290)

TabletServerGivesUpIT tests that a tserver will eventually die when it
can not write to a walog.  For walog write failures to occur, there must
be some thread in the tserver trying to write to the tserver. Changes in
elasticity have made it where the activitiy this test was doing did not
always cause a walog write.  This change is an attempt to improve the
chance of a tserver thread attempting a walog write after DFS is killed.

Author: keith-turner

test/src/main/java/org/apache/accumulo/test/TabletServerGivesUpIT.java

@@ -21,16 +21,15 @@
 import static java.util.concurrent.TimeUnit.SECONDS;
 
 import java.time.Duration;
-import java.util.TreeSet;
 import java.util.concurrent.atomic.AtomicReference;
 
 import org.apache.accumulo.core.client.Accumulo;
 import org.apache.accumulo.core.client.AccumuloClient;
 import org.apache.accumulo.core.conf.Property;
+import org.apache.accumulo.core.data.Mutation;
 import org.apache.accumulo.miniclusterImpl.MiniAccumuloConfigImpl;
 import org.apache.accumulo.test.functional.ConfigurableMacBase;
 import org.apache.hadoop.conf.Configuration;
-import org.apache.hadoop.io.Text;
 import org.junit.jupiter.api.Test;
 
 // ACCUMULO-2480
@@ -60,25 +59,40 @@ public void test() throws Exception {
       }
       final String tableName = getUniqueNames(1)[0];
       client.tableOperations().create(tableName);
+
+      // do an initial write to host the tablet and get its location in cache as we may not be able
+      // to read the metadata table later
+      try (var writer = client.createBatchWriter(tableName)) {
+        Mutation m = new Mutation("001");
+        m.put("a", "b", "c");
+        writer.addMutation(m);
+      }
+
       // Kill dfs
       cluster.getMiniDfs().shutdown();
       // ask the tserver to do something
       final AtomicReference<Exception> ex = new AtomicReference<>();
-      Thread splitter = new Thread(() -> {
+      Thread backgroundWriter = new Thread(() -> {
         try {
-          TreeSet<Text> splits = new TreeSet<>();
-          splits.add(new Text("X"));
-          client.tableOperations().addSplits(tableName, splits);
+          for (int i = 0; i < 100; i++) {
+            // These writes should cause the tserver to attempt to write to walog, which should
+            // repeatedly fail. Relying on the client side cache to have the tablet location so the
+            // writes make it to the tserver where the wal write fails.
+            try (var writer = client.createBatchWriter(tableName)) {
+              Mutation m = new Mutation("001");
+              m.put("a", "b", "c");
+              writer.addMutation(m);
+            }
+          }
         } catch (Exception e) {
           ex.set(e);
         }
       });
-      splitter.start();
+      backgroundWriter.start();
       // wait for the tserver to give up on writing to the WAL
       while (client.instanceOperations().getTabletServers().size() == 1) {
         Thread.sleep(SECONDS.toMillis(1));
       }
     }
   }
-
 }