[SPARK-15475][SQL] Add tests for writing and reading back empty data for Parquet, Json and Text data sources

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/text/TextSuite.scala

@@ -126,6 +126,22 @@ class TextSuite extends QueryTest with SharedSQLContext {
     }
   }
 
+  test("Write and read back empty data") {
+    withTempPath { path =>
+      val df = spark.read.format("text").load(testFile)
+      val emptyDf = df.limit(0)
+      emptyDf.write
+        .format("text")
+        .save(path.getCanonicalPath)
+
+      val copyEmptyDf = spark.read
+        .format("text")
+        .load(path.getCanonicalPath)
+
+      checkAnswer(emptyDf, copyEmptyDf)
+    }
+  }
+
   private def testFile: String = {
     Thread.currentThread().getContextClassLoader.getResource("text-suite.txt").toString
   }

sql/hive/src/test/scala/org/apache/spark/sql/sources/JsonHadoopFsRelationSuite.scala

@@ -108,4 +108,19 @@ class JsonHadoopFsRelationSuite extends HadoopFsRelationTest {
       )
     }
   }
+
+  test("Write and read back empty data") {
+    withTempPath { path =>
+      val emptyDf = spark.range(10).limit(0).toDF()
+      emptyDf.write
+        .format(dataSourceName)
+        .save(path.getCanonicalPath)
+
+      val copyEmptyDf = spark.read
+        .format(dataSourceName)
+        .load(path.getCanonicalPath)
+
+      assert(copyEmptyDf.count() === 0)
+    }
+  }
 }

sql/hive/src/test/scala/org/apache/spark/sql/sources/ParquetHadoopFsRelationSuite.scala

@@ -228,4 +228,19 @@ class ParquetHadoopFsRelationSuite extends HadoopFsRelationTest {
       }
     }
   }
+
+  test("Write and read back empty data") {
+    withTempPath { path =>
+      val emptyDf = spark.range(10).limit(0).toDF()
+      emptyDf.write
+        .format(dataSourceName)
+        .save(path.getCanonicalPath)
+
+      val copyEmptyDf = spark.read
+        .format(dataSourceName)
+        .load(path.getCanonicalPath)
+
+      checkAnswer(emptyDf, copyEmptyDf)
+    }
+  }
 }