Unit test for trimExceptCRLF

@jerryshao @HyukjinKwon @steveloughran

Author: gerashegalov

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -2063,7 +2063,7 @@ private[spark] object Utils extends Logging {
    * @param str
    * @return the trimmed value of str
    */
-  def trimExceptCRLF(str: String): String = {
+  private[util] def trimExceptCRLF(str: String): String = {
     val firstPos = str.indexWhere(nonSpaceOrNaturalLineDelimiter)
     val lastPos = str.lastIndexWhere(nonSpaceOrNaturalLineDelimiter)
     if (firstPos >= 0 && lastPos >= 0) {

core/src/test/scala/org/apache/spark/util/UtilsSuite.scala

@@ -1205,6 +1205,39 @@ class UtilsSuite extends SparkFunSuite with ResetSystemProperties with Logging {
     assert(Utils.stringHalfWidth("\u0967\u0968\u0969") == 3)
     // scalastyle:on nonascii
   }
+
+  test("trimExceptCRLF standalone") {
+    val crlfSet = Set("\r", "\n")
+    val nonPrintableButCRLF =
+      (0 to 32).map(_.toChar.toString).toSet -- crlfSet
+
+    // identity for CRLF
+    crlfSet
+      .foreach(s => Utils.trimExceptCRLF(s) === s)
+
+    // empty for other non-printables
+    nonPrintableButCRLF
+      .foreach(s => assert(Utils.trimExceptCRLF(s) === ""))
+
+    // identity for a printable string
+    assert(Utils.trimExceptCRLF("a") === "a")
+
+    // identity for strings with CRLF
+    crlfSet
+      .foreach { s =>
+        assert(Utils.trimExceptCRLF(s"${s}a") === s"${s}a")
+        assert(Utils.trimExceptCRLF(s"a${s}") === s"a${s}")
+        assert(Utils.trimExceptCRLF(s"b${s}b") === s"b${s}b")
+      }
+
+    // trim nonPrintableButCRLF except when inside a string
+    nonPrintableButCRLF
+      .foreach { s =>
+        assert(Utils.trimExceptCRLF(s"${s}a") === "a")
+        assert(Utils.trimExceptCRLF(s"a${s}") === "a")
+        assert(Utils.trimExceptCRLF(s"b${s}b") === s"b${s}b")
+      }
+  }
 }
 
 private class SimpleExtension