[SPARK-12321][SQL][FOLLOW-UP] Add tests for fromString

## What changes were proposed in this pull request?
Add test cases for fromString

## How was this patch tested?
N/A

Closes #22345 from gatorsmile/addTest.

Authored-by: Xiao Li <[email protected]>
Signed-off-by: gatorsmile <[email protected]>

Author: gatorsmile

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/literals.scala

@@ -128,30 +128,36 @@ object Literal {
     val dataType = DataType.parseDataType(json \ "dataType")
     json \ "value" match {
       case JNull => Literal.create(null, dataType)
-      case JString(str) =>
-        val value = dataType match {
-          case BooleanType => str.toBoolean
-          case ByteType => str.toByte
-          case ShortType => str.toShort
-          case IntegerType => str.toInt
-          case LongType => str.toLong
-          case FloatType => str.toFloat
-          case DoubleType => str.toDouble
-          case StringType => UTF8String.fromString(str)
-          case DateType => java.sql.Date.valueOf(str)
-          case TimestampType => java.sql.Timestamp.valueOf(str)
-          case CalendarIntervalType => CalendarInterval.fromString(str)
-          case t: DecimalType =>
-            val d = Decimal(str)
-            assert(d.changePrecision(t.precision, t.scale))
-            d
-          case _ => null
-        }
-        Literal.create(value, dataType)
+      case JString(str) => fromString(str, dataType)
       case other => sys.error(s"$other is not a valid Literal json value")
     }
   }
 
+  /**
+   * Constructs a Literal from a String
+   */
+  def fromString(str: String, dataType: DataType): Literal = {
+    val value = dataType match {
+      case BooleanType => str.toBoolean
+      case ByteType => str.toByte
+      case ShortType => str.toShort
+      case IntegerType => str.toInt
+      case LongType => str.toLong
+      case FloatType => str.toFloat
+      case DoubleType => str.toDouble
+      case StringType => UTF8String.fromString(str)
+      case DateType => java.sql.Date.valueOf(str)
+      case TimestampType => java.sql.Timestamp.valueOf(str)
+      case CalendarIntervalType => CalendarInterval.fromString(str)
+      case t: DecimalType =>
+        val d = Decimal(str)
+        assert(d.changePrecision(t.precision, t.scale))
+        d
+      case _ => null
+    }
+    Literal.create(value, dataType)
+  }
+
   def create(v: Any, dataType: DataType): Literal = {
     Literal(CatalystTypeConverters.convertToCatalyst(v), dataType)
   }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/LiteralExpressionSuite.scala

@@ -226,4 +226,25 @@ class LiteralExpressionSuite extends SparkFunSuite with ExpressionEvalHelper {
     checkEvaluation(Literal('\u0000'), "\u0000")
     checkEvaluation(Literal.create('\n'), "\n")
   }
+
+  test("fromString converts String/DataType input correctly") {
+    checkEvaluation(Literal.fromString(false.toString, BooleanType), false)
+    checkEvaluation(Literal.fromString(null, NullType), null)
+    checkEvaluation(Literal.fromString(Int.MaxValue.toByte.toString, ByteType), Int.MaxValue.toByte)
+    checkEvaluation(Literal.fromString(Short.MaxValue.toShort.toString, ShortType), Short.MaxValue
+      .toShort)
+    checkEvaluation(Literal.fromString(Int.MaxValue.toString, IntegerType), Int.MaxValue)
+    checkEvaluation(Literal.fromString(Long.MaxValue.toString, LongType), Long.MaxValue)
+    checkEvaluation(Literal.fromString(Float.MaxValue.toString, FloatType), Float.MaxValue)
+    checkEvaluation(Literal.fromString(Double.MaxValue.toString, DoubleType), Double.MaxValue)
+    checkEvaluation(Literal.fromString("1.23456", DecimalType(10, 5)), Decimal(1.23456))
+    checkEvaluation(Literal.fromString("Databricks", StringType), "Databricks")
+    val dateString = "1970-01-01"
+    checkEvaluation(Literal.fromString(dateString, DateType), java.sql.Date.valueOf(dateString))
+    val timestampString = "0000-01-01 00:00:00"
+    checkEvaluation(Literal.fromString(timestampString, TimestampType),
+      java.sql.Timestamp.valueOf(timestampString))
+    val calInterval = new CalendarInterval(1, 1)
+    checkEvaluation(Literal.fromString(calInterval.toString, CalendarIntervalType), calInterval)
+  }
 }