Add back assertions removed by LUCENE-9187. (#1236)

This time they would only apply to TestFastLZ4/TestHighLZ4 and avoid slowing
down all tests.

lucene/core/src/java/org/apache/lucene/util/compress/LZ4.java

@@ -203,6 +203,9 @@ public final class LZ4 {
      * offsets. A return value of {@code -1} indicates that no other index could
      * be found. */
     abstract int previous(int off);
+
+    // For testing
+    abstract boolean assertReset();
   }
 
   /**
@@ -264,6 +267,11 @@ public final class LZ4 {
       return -1;
     }
 
+    @Override
+    boolean assertReset() {
+      return true;
+    }
+
   }
 
   /**
@@ -370,6 +378,14 @@ public final class LZ4 {
       }
       return -1;
     }
+
+    @Override
+    boolean assertReset() {
+      for (int i = 0; i < chainTable.length; ++i) {
+        assert chainTable[i] == (short) 0xFFFF : i;
+      }
+      return true;
+    }
   }
 
   /**

lucene/core/src/test/org/apache/lucene/util/compress/LZ4TestCase.java

@@ -30,6 +30,37 @@ public abstract class LZ4TestCase extends LuceneTestCase {
 
   protected abstract LZ4.HashTable newHashTable();
 
+  protected static class AssertingHashTable extends LZ4.HashTable {
+
+    private final LZ4.HashTable in;
+
+    AssertingHashTable(LZ4.HashTable in) {
+      this.in = in;
+    }
+
+    @Override
+    void reset(byte[] b, int off, int len) {
+      in.reset(b, off, len);
+      assertTrue(in.assertReset());
+    }
+
+    @Override
+    int get(int off) {
+      return in.get(off);
+    }
+
+    @Override
+    int previous(int off) {
+      return in.previous(off);
+    }
+
+    @Override
+    boolean assertReset() {
+      throw new UnsupportedOperationException();
+    }
+
+  }
+
   private void doTest(byte[] data, LZ4.HashTable hashTable) throws IOException {
     int offset = random().nextBoolean()
         ? random().nextInt(10)

lucene/core/src/test/org/apache/lucene/util/compress/TestFastLZ4.java

@@ -22,7 +22,8 @@ public class TestFastLZ4 extends LZ4TestCase {
 
   @Override
   protected HashTable newHashTable() {
-    return new LZ4.FastCompressionHashTable();
+    LZ4.HashTable hashTable = new LZ4.FastCompressionHashTable();
+    return new AssertingHashTable(hashTable);
   }
 
 }

lucene/core/src/test/org/apache/lucene/util/compress/TestHighLZ4.java

@@ -22,7 +22,8 @@ public class TestHighLZ4 extends LZ4TestCase {
 
   @Override
   protected HashTable newHashTable() {
-    return new LZ4.HighCompressionHashTable();
+    LZ4.HashTable hashTable =  new LZ4.HighCompressionHashTable();
+    return new AssertingHashTable(hashTable);
   }
 
 }