Add tests for Lucene90PostingsFormat back (#12904)

I just noticed that the move from FOR to PFOR did all the work to make the old
format (FOR) writeable, but missed keeping an instance of
`BasePostingsFormatTestCase` for this format.

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene90/TestLucene90PostingsFormat.java

@@ -0,0 +1,148 @@
+/*
+ * 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.lucene90;
+
+import static org.apache.lucene.backward_codecs.lucene90.Lucene90ScoreSkipReader.readImpacts;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import org.apache.lucene.backward_codecs.lucene90.Lucene90ScoreSkipReader.MutableImpactList;
+import org.apache.lucene.codecs.Codec;
+import org.apache.lucene.codecs.CompetitiveImpactAccumulator;
+import org.apache.lucene.codecs.lucene90.blocktree.FieldReader;
+import org.apache.lucene.codecs.lucene90.blocktree.Stats;
+import org.apache.lucene.codecs.lucene99.Lucene99PostingsFormat;
+import org.apache.lucene.codecs.lucene99.Lucene99SkipWriter;
+import org.apache.lucene.document.Document;
+import org.apache.lucene.document.Field;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.Impact;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.store.ByteArrayDataInput;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IOContext;
+import org.apache.lucene.store.IndexInput;
+import org.apache.lucene.store.IndexOutput;
+import org.apache.lucene.tests.analysis.MockAnalyzer;
+import org.apache.lucene.tests.index.BasePostingsFormatTestCase;
+import org.apache.lucene.tests.util.TestUtil;
+
+public class TestLucene90PostingsFormat extends BasePostingsFormatTestCase {
+  private final Codec codec = TestUtil.alwaysPostingsFormat(new Lucene90RWPostingsFormat());
+
+  @Override
+  protected Codec getCodec() {
+    return codec;
+  }
+
+  /** Make sure the final sub-block(s) are not skipped. */
+  public void testFinalBlock() throws Exception {
+    Directory d = newDirectory();
+    IndexWriter w = new IndexWriter(d, new IndexWriterConfig(new MockAnalyzer(random())));
+    for (int i = 0; i < 25; i++) {
+      Document doc = new Document();
+      doc.add(newStringField("field", Character.toString((char) (97 + i)), Field.Store.NO));
+      doc.add(newStringField("field", "z" + Character.toString((char) (97 + i)), Field.Store.NO));
+      w.addDocument(doc);
+    }
+    w.forceMerge(1);
+
+    DirectoryReader r = DirectoryReader.open(w);
+    assertEquals(1, r.leaves().size());
+    FieldReader field = (FieldReader) r.leaves().get(0).reader().terms("field");
+    // We should see exactly two blocks: one root block (prefix empty string) and one block for z*
+    // terms (prefix z):
+    Stats stats = field.getStats();
+    assertEquals(0, stats.floorBlockCount);
+    assertEquals(2, stats.nonFloorBlockCount);
+    r.close();
+    w.close();
+    d.close();
+  }
+
+  private void shouldFail(int minItemsInBlock, int maxItemsInBlock) {
+    expectThrows(
+        IllegalArgumentException.class,
+        () -> {
+          new Lucene99PostingsFormat(minItemsInBlock, maxItemsInBlock);
+        });
+  }
+
+  public void testInvalidBlockSizes() throws Exception {
+    shouldFail(0, 0);
+    shouldFail(10, 8);
+    shouldFail(-1, 10);
+    shouldFail(10, -1);
+    shouldFail(10, 12);
+  }
+
+  public void testImpactSerialization() throws IOException {
+    // omit norms and omit freqs
+    doTestImpactSerialization(Collections.singletonList(new Impact(1, 1L)));
+
+    // omit freqs
+    doTestImpactSerialization(Collections.singletonList(new Impact(1, 42L)));
+    // omit freqs with very large norms
+    doTestImpactSerialization(Collections.singletonList(new Impact(1, -100L)));
+
+    // omit norms
+    doTestImpactSerialization(Collections.singletonList(new Impact(30, 1L)));
+    // omit norms with large freq
+    doTestImpactSerialization(Collections.singletonList(new Impact(500, 1L)));
+
+    // freqs and norms, basic
+    doTestImpactSerialization(
+        Arrays.asList(
+            new Impact(1, 7L),
+            new Impact(3, 9L),
+            new Impact(7, 10L),
+            new Impact(15, 11L),
+            new Impact(20, 13L),
+            new Impact(28, 14L)));
+
+    // freqs and norms, high values
+    doTestImpactSerialization(
+        Arrays.asList(
+            new Impact(2, 2L),
+            new Impact(10, 10L),
+            new Impact(12, 50L),
+            new Impact(50, -100L),
+            new Impact(1000, -80L),
+            new Impact(1005, -3L)));
+  }
+
+  private void doTestImpactSerialization(List<Impact> impacts) throws IOException {
+    CompetitiveImpactAccumulator acc = new CompetitiveImpactAccumulator();
+    for (Impact impact : impacts) {
+      acc.add(impact.freq, impact.norm);
+    }
+    try (Directory dir = newDirectory()) {
+      try (IndexOutput out = dir.createOutput("foo", IOContext.DEFAULT)) {
+        Lucene99SkipWriter.writeImpacts(acc, out);
+      }
+      try (IndexInput in = dir.openInput("foo", IOContext.DEFAULT)) {
+        byte[] b = new byte[Math.toIntExact(in.length())];
+        in.readBytes(b, 0, b.length);
+        List<Impact> impacts2 = readImpacts(new ByteArrayDataInput(b), new MutableImpactList());
+        assertEquals(impacts, impacts2);
+      }
+    }
+  }
+}