[multistage] add test for LiteralValueOperator (#9796)

* add test for LiteralValueOperator
* add empty tests

pinot-query-runtime/src/test/java/org/apache/pinot/query/runtime/operator/LiteralValueOperatorTest.java

@@ -0,0 +1,71 @@
+/**
+ * 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.pinot.query.runtime.operator;
+
+import com.google.common.collect.ImmutableList;
+import java.util.List;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.common.utils.DataSchema.ColumnDataType;
+import org.apache.pinot.query.planner.logical.RexExpression;
+import org.apache.pinot.query.runtime.blocks.TransferableBlock;
+import org.apache.pinot.spi.data.FieldSpec.DataType;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+
+public class LiteralValueOperatorTest {
+
+  @Test
+  public void shouldReturnLiteralBlock() {
+    // Given:
+    DataSchema schema = new DataSchema(new String[]{"sLiteral", "iLiteral"},
+        new ColumnDataType[]{ColumnDataType.STRING, ColumnDataType.INT});
+    List<List<RexExpression>> literals = ImmutableList.of(
+        ImmutableList.of(
+            new RexExpression.Literal(DataType.STRING, "foo"),
+            new RexExpression.Literal(DataType.INT, 1)),
+        ImmutableList.of(
+            new RexExpression.Literal(DataType.STRING, ""),
+            new RexExpression.Literal(DataType.INT, 2))
+    );
+    LiteralValueOperator operator = new LiteralValueOperator(schema, literals);
+
+    // When:
+    TransferableBlock transferableBlock = operator.nextBlock();
+
+    // Then:
+    Assert.assertEquals(transferableBlock.getContainer().get(0), new Object[]{"foo", 1});
+    Assert.assertEquals(transferableBlock.getContainer().get(1), new Object[]{"", 2});
+    Assert.assertTrue(operator.nextBlock().isEndOfStreamBlock(), "Expected EOS after reading two rows");
+  }
+
+  @Test
+  public void shouldHandleEmptyLiteralRows() {
+    // Given:
+    DataSchema schema = new DataSchema(new String[]{}, new ColumnDataType[]{});
+    List<List<RexExpression>> literals = ImmutableList.of(ImmutableList.of());
+    LiteralValueOperator operator = new LiteralValueOperator(schema, literals);
+
+    // When:
+    TransferableBlock transferableBlock = operator.nextBlock();
+
+    // Then:
+    Assert.assertEquals(transferableBlock.getContainer().get(0), new Object[]{});
+  }
+}