Added UT for leastRestrictiveVarbinaryVarchar

Signed-off-by: Vinay Krishna Pudyodu <vinkrish.neo@gmail.com>

Author: vinaykpud

core/src/test/java/org/opensearch/sql/calcite/utils/OpenSearchTypeFactoryTest.java

@@ -6,6 +6,7 @@
 package org.opensearch.sql.calcite.utils;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -128,6 +129,123 @@ public void testLeastRestrictiveDelegatesToSuperForPlainTypes() {
     assertEquals(SqlTypeName.INTEGER, result.getSqlTypeName());
   }
 
+  @Test
+  public void testLeastRestrictiveVarbinaryAndVarcharReturnsVarbinary() {
+    RelDataType varbinary = TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY);
+    RelDataType varchar = TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR);
+
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(varbinary, varchar));
+
+    assertNotNull(result);
+    assertEquals(SqlTypeName.VARBINARY, result.getSqlTypeName());
+    assertFalse(result.isNullable());
+  }
+
+  @Test
+  public void testLeastRestrictiveVarcharAndVarbinaryReturnsVarbinary() {
+    RelDataType varchar = TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR);
+    RelDataType varbinary = TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY);
+
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(varchar, varbinary));
+
+    assertNotNull(result);
+    assertEquals(SqlTypeName.VARBINARY, result.getSqlTypeName());
+  }
+
+  @Test
+  public void testLeastRestrictiveVarbinaryAndCharReturnsVarbinary() {
+    RelDataType varbinary = TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY);
+    RelDataType ch = TYPE_FACTORY.createSqlType(SqlTypeName.CHAR);
+
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(varbinary, ch));
+
+    assertNotNull(result);
+    assertEquals(SqlTypeName.VARBINARY, result.getSqlTypeName());
+  }
+
+  @Test
+  public void testLeastRestrictiveVarbinaryAndMultipleVarcharLiteralsReturnsVarbinary() {
+    RelDataType varbinary = TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY);
+    RelDataType v1 = TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR);
+    RelDataType v2 = TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR);
+
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(varbinary, v1, v2));
+
+    assertNotNull(result);
+    assertEquals(SqlTypeName.VARBINARY, result.getSqlTypeName());
+  }
+
+  @Test
+  public void testLeastRestrictiveVarbinaryAndNullableVarcharReturnsNullableVarbinary() {
+    RelDataType varbinary = TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY);
+    RelDataType nullableVarchar =
+        TYPE_FACTORY.createTypeWithNullability(
+            TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR), true);
+
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(varbinary, nullableVarchar));
+
+    assertNotNull(result);
+    assertEquals(SqlTypeName.VARBINARY, result.getSqlTypeName());
+    assertTrue(result.isNullable());
+  }
+
+  @Test
+  public void testLeastRestrictiveNullableVarbinaryAndVarcharReturnsNullableVarbinary() {
+    RelDataType nullableVarbinary =
+        TYPE_FACTORY.createTypeWithNullability(
+            TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY), true);
+    RelDataType varchar = TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR);
+
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(nullableVarbinary, varchar));
+
+    assertNotNull(result);
+    assertEquals(SqlTypeName.VARBINARY, result.getSqlTypeName());
+    assertTrue(result.isNullable());
+  }
+
+  @Test
+  public void testLeastRestrictiveTwoVarbinariesReturnsVarbinary() {
+    RelDataType v1 = TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY);
+    RelDataType v2 = TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY);
+
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(v1, v2));
+
+    assertNotNull(result);
+    assertEquals(SqlTypeName.VARBINARY, result.getSqlTypeName());
+  }
+
+  @Test
+  public void testLeastRestrictiveVarbinaryAndIntegerFallsBackToSuper() {
+    RelDataType varbinary = TYPE_FACTORY.createSqlType(SqlTypeName.VARBINARY);
+    RelDataType integer = TYPE_FACTORY.createSqlType(SqlTypeName.INTEGER);
+
+    // Mixing VARBINARY with a non-string type — varbinary/varchar coercion does not apply,
+    // so this falls back to super.leastRestrictive (which returns null for incompatible types).
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(varbinary, integer));
+
+    // super.leastRestrictive cannot find a common type for VARBINARY + INTEGER
+    // The exact behavior depends on Calcite's type system, but the key check is that
+    // we did NOT return VARBINARY from leastRestrictiveVarbinaryVarchar.
+    if (result != null) {
+      assertFalse(
+          result.getSqlTypeName() == SqlTypeName.VARBINARY,
+          "VARBINARY + INTEGER should not coerce to VARBINARY via the varbinary/varchar path");
+    }
+  }
+
+  @Test
+  public void testLeastRestrictiveOnlyVarcharsReturnsVarchar() {
+    RelDataType v1 = TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR);
+    RelDataType v2 = TYPE_FACTORY.createSqlType(SqlTypeName.VARCHAR);
+
+    // No VARBINARY in list — leastRestrictiveVarbinaryVarchar returns null,
+    // so super.leastRestrictive resolves to VARCHAR.
+    RelDataType result = TYPE_FACTORY.leastRestrictive(List.of(v1, v2));
+
+    assertNotNull(result);
+    assertEquals(SqlTypeName.VARCHAR, result.getSqlTypeName());
+  }
+
   @Test
   public void testConvertSqlTypeNameVarbinaryToBinaryExprType() {
     assertEquals(