Added LogicalHighlightTest and removed check for instance of Highligh…

…tFunction in Analyzer as this case should not be reachable.

Signed-off-by: forestmvey <forestv@bitquilltech.com>

core/src/main/java/org/opensearch/sql/analysis/Analyzer.java

@@ -342,10 +342,6 @@ public LogicalPlan visitEval(Eval node, AnalysisContext context) {
   public LogicalPlan visitHighlight(Highlight node, AnalysisContext context) {
     LogicalPlan child = node.getChild().get(0).accept(this, context);
 
-    if (!(((Alias)node.getExpression()).getDelegated() instanceof HighlightFunction)) {
-      return null;
-    }
-
     // Replace all single quotes with double quotes for parsing mapping in HighlightOperator
     TypeEnvironment env = context.peek();
     env.define(new Symbol(Namespace.FIELD_NAME,

core/src/test/java/org/opensearch/sql/planner/logical/LogicalHighlightTest.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright OpenSearch Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.opensearch.sql.planner.logical;
+
+import static org.opensearch.sql.ast.dsl.AstDSL.alias;
+import static org.opensearch.sql.ast.dsl.AstDSL.highlight;
+import static org.opensearch.sql.ast.dsl.AstDSL.relation;
+import static org.opensearch.sql.ast.dsl.AstDSL.stringLiteral;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.opensearch.sql.analysis.AnalyzerTestBase;
+import org.opensearch.sql.ast.tree.Highlight;
+import org.opensearch.sql.expression.DSL;
+import org.opensearch.sql.expression.config.ExpressionConfig;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+@Configuration
+@ExtendWith(SpringExtension.class)
+@ContextConfiguration(classes = {ExpressionConfig.class, AnalyzerTestBase.class})
+@ExtendWith(MockitoExtension.class)
+public class LogicalHighlightTest extends AnalyzerTestBase {
+  @Test
+  public void analyze_highlight_with_one_field() {
+    assertAnalyzeEqual(
+        LogicalPlanDSL.highlight(
+            LogicalPlanDSL.relation("schema"),
+            DSL.literal("field")),
+        new Highlight(
+            alias("highlight('field')",
+                highlight(stringLiteral("field"))))
+            .attach(relation("schema")));
+  }
+}