fixup! fixup! added tests for empty delimStr, csv and tsv

Author: Jolanrensen

core/src/test/kotlin/org/jetbrains/kotlinx/dataframe/io/CsvTests.kt

@@ -8,11 +8,13 @@ import org.apache.commons.csv.CSVFormat
 import org.jetbrains.kotlinx.dataframe.DataFrame
 import org.jetbrains.kotlinx.dataframe.api.ParserOptions
 import org.jetbrains.kotlinx.dataframe.api.allNulls
+import org.jetbrains.kotlinx.dataframe.api.append
 import org.jetbrains.kotlinx.dataframe.api.convert
 import org.jetbrains.kotlinx.dataframe.api.dataFrameOf
 import org.jetbrains.kotlinx.dataframe.api.group
 import org.jetbrains.kotlinx.dataframe.api.groupBy
 import org.jetbrains.kotlinx.dataframe.api.into
+import org.jetbrains.kotlinx.dataframe.api.isEmpty
 import org.jetbrains.kotlinx.dataframe.api.schema
 import org.jetbrains.kotlinx.dataframe.api.toStr
 import org.jetbrains.kotlinx.dataframe.ncol
@@ -297,12 +299,20 @@ class CsvTests {
             file = File.createTempFile("empty", "csv"),
             header = listOf("a", "b", "c"),
         )
-        emptyCsvFileManualHeader shouldBe dataFrameOf("a", "b", "c").fill(0) { "" }
+        emptyCsvFileManualHeader.apply {
+            isEmpty() shouldBe true
+            columnNames() shouldBe listOf("a", "b", "c")
+            columnTypes() shouldBe listOf(typeOf<String>(), typeOf<String>(), typeOf<String>())
+        }
 
         val emptyCsvFileWithHeader = DataFrame.readCSV(
             file = File.createTempFile("empty", "csv").also { it.writeText("a,b,c") },
         )
-        emptyCsvFileWithHeader shouldBe dataFrameOf("a", "b", "c").fill(0) { "" }
+        emptyCsvFileWithHeader.apply {
+            isEmpty() shouldBe true
+            columnNames() shouldBe listOf("a", "b", "c")
+            columnTypes() shouldBe listOf(typeOf<String>(), typeOf<String>(), typeOf<String>())
+        }
 
         val emptyTsvStr = DataFrame.readTSV(File.createTempFile("empty", "tsv"))
         emptyTsvStr shouldBe DataFrame.empty()