Remove write logic from Lucene70NormsFormat. (#2287)

Our policy is to not maintain write logic for old formats that can't be written
to. The write logic is moved to the test folder to support unit testing.

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene70/Lucene70Codec.java

@@ -134,7 +134,7 @@ public class Lucene70Codec extends Codec {
   private final NormsFormat normsFormat = new Lucene70NormsFormat();
 
   @Override
-  public final NormsFormat normsFormat() {
+  public NormsFormat normsFormat() {
     return normsFormat;
   }
 }

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene70/Lucene70NormsFormat.java

@@ -87,8 +87,7 @@ public class Lucene70NormsFormat extends NormsFormat {
 
   @Override
   public NormsConsumer normsConsumer(SegmentWriteState state) throws IOException {
-    return new Lucene70NormsConsumer(
-        state, DATA_CODEC, DATA_EXTENSION, METADATA_CODEC, METADATA_EXTENSION);
+    throw new UnsupportedOperationException("Old codecs may only be used for reading");
   }
 
   @Override
@@ -97,10 +96,10 @@ public class Lucene70NormsFormat extends NormsFormat {
         state, DATA_CODEC, DATA_EXTENSION, METADATA_CODEC, METADATA_EXTENSION);
   }
 
-  private static final String DATA_CODEC = "Lucene70NormsData";
-  private static final String DATA_EXTENSION = "nvd";
-  private static final String METADATA_CODEC = "Lucene70NormsMetadata";
-  private static final String METADATA_EXTENSION = "nvm";
+  static final String DATA_CODEC = "Lucene70NormsData";
+  static final String DATA_EXTENSION = "nvd";
+  static final String METADATA_CODEC = "Lucene70NormsMetadata";
+  static final String METADATA_EXTENSION = "nvm";
   static final int VERSION_START = 0;
   static final int VERSION_CURRENT = VERSION_START;
 }

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene70/Lucene70RWCodec.java

@@ -18,6 +18,7 @@ package org.apache.lucene.backward_codecs.lucene70;
 
 import org.apache.lucene.backward_codecs.lucene50.Lucene50RWPostingsFormat;
 import org.apache.lucene.backward_codecs.lucene50.Lucene50RWStoredFieldsFormat;
+import org.apache.lucene.codecs.NormsFormat;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.SegmentInfoFormat;
 import org.apache.lucene.codecs.StoredFieldsFormat;
@@ -43,6 +44,11 @@ public final class Lucene70RWCodec extends Lucene70Codec {
     return new Lucene70RWSegmentInfoFormat();
   }
 
+  @Override
+  public NormsFormat normsFormat() {
+    return new Lucene70RWNormsFormat();
+  }
+
   @Override
   public StoredFieldsFormat storedFieldsFormat() {
     return new Lucene50RWStoredFieldsFormat();

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene70/Lucene70RWNormsFormat.java

@@ -0,0 +1,30 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.backward_codecs.lucene70;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.NormsConsumer;
+import org.apache.lucene.index.SegmentWriteState;
+
+public class Lucene70RWNormsFormat extends Lucene70NormsFormat {
+
+  @Override
+  public NormsConsumer normsConsumer(SegmentWriteState state) throws IOException {
+    return new Lucene70NormsConsumer(
+        state, DATA_CODEC, DATA_EXTENSION, METADATA_CODEC, METADATA_EXTENSION);
+  }
+}