[SPARK-26745][SQL][TESTS] JsonSuite test case: empty line -> 0 record count

This PR consists of the `test` components of #23665 only, minus the associated patch from that PR.

It adds a new unit test to `JsonSuite` which verifies that the `count()` returned from a `DataFrame` loaded from JSON containing empty lines does not include those empty lines in the record count. The test runs `count` prior to otherwise reading data from the `DataFrame`, so as to catch future cases where a pre-parsing optimization might result in `count` results inconsistent with existing behavior.

This PR is intended to be deployed alongside #23667; `master` currently causes the test to fail, as described in [SPARK-26745](https://issues.apache.org/jira/browse/SPARK-26745).

Manual testing, existing `JsonSuite` unit tests.

Closes #23674 from sumitsu/json_emptyline_count_test.

Authored-by: Branden Smith <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>
(cherry picked from commit 63bced9)
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: Branden Smith

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

@@ -2515,4 +2515,16 @@ class JsonSuite extends QueryTest with SharedSQLContext with TestJsonData {
     checkCount(2)
     countForMalformedJSON(0, Seq(""))
   }
+
+  test("SPARK-26745: count() for non-multiline input with empty lines") {
+    withTempPath { tempPath =>
+      val path = tempPath.getCanonicalPath
+      Seq("""{ "a" : 1 }""", "", """     { "a" : 2 }""", " \t ")
+        .toDS()
+        .repartition(1)
+        .write
+        .text(path)
+      assert(spark.read.json(path).count() === 2)
+    }
+  }
 }