[SPARK-23094][SPARK-23723][SPARK-23724][SQL][FOLLOW-UP] Support custom encoding for json files

## What changes were proposed in this pull request?
This is to add a test case to check the behaviors when users write json in the specified UTF-16/UTF-32 encoding with multiline off.

## How was this patch tested?
N/A

Author: gatorsmile <gatorsmile@gmail.com>

Closes #21254 from gatorsmile/followupSPARK-23094.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/json/JSONOptions.scala

@@ -110,11 +110,12 @@ private[sql] class JSONOptions(
       val blacklist = Seq(Charset.forName("UTF-16"), Charset.forName("UTF-32"))
       val isBlacklisted = blacklist.contains(Charset.forName(enc))
       require(multiLine || !isBlacklisted,
-        s"""The ${enc} encoding must not be included in the blacklist when multiLine is disabled:
-           | ${blacklist.mkString(", ")}""".stripMargin)
+        s"""The $enc encoding in the blacklist is not allowed when multiLine is disabled.
+          |Blacklist: ${blacklist.mkString(", ")}""".stripMargin)
+
+      val isLineSepRequired =
+        multiLine || Charset.forName(enc) == StandardCharsets.UTF_8 || lineSeparator.nonEmpty
 
-      val isLineSepRequired = !(multiLine == false &&
-        Charset.forName(enc) != StandardCharsets.UTF_8 && lineSeparator.isEmpty)
       require(isLineSepRequired, s"The lineSep option must be specified for the $enc encoding")
 
       enc

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/json/JsonSuite.scala

@@ -2313,6 +2313,25 @@ class JsonSuite extends QueryTest with SharedSQLContext with TestJsonData {
     }
   }
 
+  test("SPARK-23723: write json in UTF-16/32 with multiline off") {
+    Seq("UTF-16", "UTF-32").foreach { encoding =>
+      withTempPath { path =>
+        val ds = spark.createDataset(Seq(
+          ("a", 1), ("b", 2), ("c", 3))
+        ).repartition(2)
+        val e = intercept[IllegalArgumentException] {
+          ds.write
+            .option("encoding", encoding)
+            .option("multiline", "false")
+            .format("json").mode("overwrite")
+            .save(path.getCanonicalPath)
+        }.getMessage
+        assert(e.contains(
+          s"$encoding encoding in the blacklist is not allowed when multiLine is disabled"))
+      }
+    }
+  }
+
   def checkReadJson(lineSep: String, encoding: String, inferSchema: Boolean, id: Int): Unit = {
     test(s"SPARK-23724: checks reading json in ${encoding} #${id}") {
       val schema = new StructType().add("f1", StringType).add("f2", IntegerType)