HBASE-29729 Add integration test

Author: Alex Hughes

hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionServerMetrics.java

@@ -18,6 +18,7 @@
 package org.apache.hadoop.hbase.regionserver;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
@@ -598,4 +599,21 @@ public void testReadBytes() throws Exception {
     assertEquals("Total zero-byte read bytes should be equal to 0", 0,
       metricsRegionServer.getRegionServerWrapper().getZeroCopyBytesRead());
   }
+
+  @Test
+  public void testTableDescriptorHashMetric() throws Exception {
+    doNPuts(1, false);
+    metricsRegionServer.getRegionServerWrapper().forceRecompute();
+
+    HRegion region = rs.getRegions(tableName).get(0);
+    assertNotNull("Region should exist", region);
+
+    try (MetricsRegionWrapperImpl wrapper = new MetricsRegionWrapperImpl(region)) {
+      String hash = wrapper.getTableDescriptorHash();
+
+      assertNotNull("TableDescriptorHash should not be null", hash);
+      assertNotEquals("TableDescriptorHash should not be 'UNKNOWN'", "UNKNOWN", hash);
+      assertEquals("Hash should be 64 characters (SHA-256 hex)", 64, hash.length());
+    }
+  }
 }